Sadly, some parents can be afraid to tell their children what they intend to do with their assets in their will for fear of upsetting them and creating family divisions.
"Some parents may be concerned that if they discuss their testamentary intentions with their children that the child they are most dependent upon may be disappointed," explained Mr Faughnan. "They may therefore be afraid of alienating themselves from that child and for that reason they may decide not to discuss their testamentary intentions.
"Parents know their children best and they may decide that it is in the family's interest in general not to discuss their will while alive," he said.
Where a person is not of 'sound mind' or where they lacked testamentary capacity, the will can be set aside by the court and the second-last will (if one exists) shall become the last will and testament. However, if no earlier will exists then the person will be deemed to have died intestate.
Where there is no earlier will, the estate is divided according to the rules of intestacy (see Part Two of this series next week).
"Advances in medicine and our understanding of cognitive impairment have made these types of challenge more common in the courts," explained Mr Faughnan.
A will may be declared invalid if the person who wrote it was pressurised, coerced or forced into writing their will in a particular way by another party. Duress involves proving coercion.
Duress and undue influence can occur where vulnerable, elderly people may rely heavily on someone, perhaps a son or daughter, to help them every day. In these scenarios, the elderly person can be coerced into leaving their estate to that person.
Undue influence is one of the reasons why a solicitor should insist that everyone other than the legal advisors leaves the room when the instructions for the will are being taken and when the will is being executed.
"It is not uncommon for wills to be challenged on the grounds of duress but this challenge is usually coupled with a claim that the deceased lacked the required testamentary capacity to make his or her will on a particular date," said Mr Faughnan.
"The onus rests on the person making the allegation to prove duress or undue influence.
"He must name the individual against whom the charge is made, specify the conduct that constitutes duress or undue influence and specify where and when the alleged conduct took place."
Legal right share
There are some restrictions on what you can do in a will. In general, you may not completely disinherit a spouse/civil partner and, if you do, your spouse/civil partner may claim what is known as their legal right share.
Where a person dies a will, the spouse or civil partner is entitled to one half of the estate, provided there are no children. If there are children, the spouse or civil partner is entitled to one-third of the estate.
The children are not necessarily entitled to the remainder of the estate.
The legal right share came about as part of the Succession Act 1965. Up to the 1960s, a spouse was free to dispose of their property as they saw fit as long as they were mentally competent.
At that time, a farmer often left the property to one son to the exclusion of his wife and other children.
However, Charlie Haughey, as minister for justice, wanted to prevent this discrimination against women in inheritance rights. He argued that the right to disinherit a spouse in the family was unacceptable.
The legal right share was enshrined in the Succession Act 1965, guaranteeing that in a marriage, the widow/widower would still have rights, no matter what was written in the will.
Section 117 claims
Under the Succession Act, Section 117 says that if a parent fails in his or her moral duty to make 'proper provision' for a child, then the court can order that provision be made for the child from the deceased parent's estate (as long as it does not affect the legal right share of the surviving spouse).
The court must consider the matter from the point of view of a prudent and just parent, taking into account the position of each child and any other relevant circumstances. It is up to the child to prove that their parent failed in their moral duty.
A 2003 High Court ruling by Mr Justice Nicholas Kearns (now president of the High Court) highlighted several key legal points about Section 117 claims.
He noted that Section 117 does not create an obligation to leave something to each child and the provision of an expensive education or the provision of gifts/settlements to a child during the testator's lifetime might discharge the moral duty under Section 117.
He also noted that special circumstances may give rise to a moral duty. For example, if a child was induced to believe that by working the farm, that they would become the ultimate owner of it.
"The date for deciding whether or not a parent failed in his or her moral duty to a child is the date of death of the parent. So it is good practice for parents to review their will every two years," advised Mr Faughnan.
"A will written by a parent in 1986 dividing all of the assets equally between five children may, at the time, be a discharge of their moral duty because at that time all five children were in good health, had a good education, good prospects in the future," he explained.
"However, their circumstances may have changed for the better or worse before the parent dies in 2013.
"For example, if one child developed a serious illness, received no income and had poor prospects into the future, then in those circumstances, equal division of the estate between the five children may amount to a failure in the moral duty to that particular child.
"The court may decide that greater provision should have been made for that child and proceed to make what it regards as proper provision for that child. Each case is judged on its own facts and no two cases are the same."
Legitimate expectation or Breach of promise
In rural areas, another reason for a will to be challenged is for when someone who works on a farm for a long period, often without pay, in the expectation that they will inherit the farm.
The principle of 'proprietary estoppel' means that if you have relied on a promise made to you that you will gain a particular asset upon the death of a person and the person then makes a will effectively breaking the promise, the will can be challenged in the courts.
The 2012 High Court case of Naylor vs Maher (see Case Study below) is one example of a will being successfully challenged on the grounds of legitimate expectation.
The decision is now under appeal to the Supreme Court.
Next week, in Part Two of this three-part series of farm business issues, we look at what happens when no will is made and examine the dangers of DIY wills. The final week will look at best practice when it comes to having the succession conversation.
Readers should always seek professional legal advice when writing a will.
Case Study: Breach of promise in Naylor v Maher farm case
Naylor v Maher --  IEHC 408
This case concerned a legal challenge by 57-year-old William Naylor to a will written by Mr Michael Hoare in 2006, who he believed to be his stepfather, but who during the course of the trial was proved to be his father.
In the 2006 will, Mr Hoare left his 120ac farm at Derrylahan, Roscrea, Co Tipperary to his daughter Jean Maher, the defendant, who nursed him prior to his death.
However, Mr Hoare had made a will in 2005 in which he left the 120ac to the plaintiff, Mr Naylor. William Naylor claimed he was entitled to the lands on two grounds.
The first was that in the 1970s, he and Mr Hoare had agreed that if Mr Naylor carried out work on the farm and provided services both on the farm and to Mr Hoare personally for minimal pay then he, Mr Hoare, would make a will leaving the 120ac to Mr Naylor.
Mr Naylor claimed that from around 1973 onwards, Mr Hoare told him several times that Mr Naylor was working the lands for himself and that they would "one day be his".
Mr Naylor worked on Mr Hoare's farm from a very young age, starting with rearing calves and pigs and moving to milking the cows by the age of 13.
He claimed that anytime he approached Mr Hoare about pay for his work, Mr Hoare would say: "Why would I pay you? Sure this place is going to be yours anyway."
Mr Naylor told the court that he had held up his side of the agreement but Mr Hoare had breached it by not leaving him the 120ac.
Mr Naylor's second reason for challenging the 2006 will was that he claimed it was null and void because it was procured by reason of duress or undue influence being exerted upon the deceased by Jean Maher. Mr Naylor claimed Mr Hoare had not been acting freely and voluntarily when he made his 2006 will and that the earlier 2005 will under which he would receive the land should stand.
In the High Court, Mr Justice Daniel O'Keeffe held that the 2006 will was not procured by reason of duress or undue influence being exercised upon Mr Hoare by Jean Maher.
However, he did agree that Mr Hoare had breached the agreement and had reneged on his representations to Mr Naylor.
Mr Justice O'Keeffe said Mr Naylor had acted to his detriment by working the lands for more than 30 years for minimal pay and had been induced to do so by the promises made by Mr Hoare and, therefore, the court would enforce the agreement made between them.
The case is currently under appeal to the Supreme Court.