Four Irish siblings detained by Egyptian authorities are expected to face a prosecutor today.
Sisters Omaima, 20, Fatima, 22, and Somaia, 27, and their 17-year-old brother Ibrihim, were caught up in violence in the Egyptian capital and jailed in Tora prison earlier this month.
The department has been providing consular assistance to the siblings, from Firhouse, south Dublin.
They are believed to be in good health.
The Halawas had travelled to Egypt earlier in the summer for a holiday.
They were forced to seek sanctuary in the Al Fateh mosque nearly two weeks ago after violent clashes between supporters of ousted president Mohammed Morsi and the security forces killed around 80 people.
The siblings' sister Khadija Halawa said the family was hoping to get good news from the meeting at the prosecutor's office.
But she warned she is not very optimistic, because they had received "bad treatment" before.
"We are hoping for good news, but to be honest, because of the situation in Cairo now, we're not very sure of what is going to happen," Ms Halawa said.
"They have not told us exactly will they be held with them again or will they be let free."
It is understood the three sisters and their teenage brother have been detained in separate holdings.
Ms Halawa said she expected them to be reunited for their appearance today, when their lawyers are likely to be present.
She said the family also learned that prisoners had been given charge sheets and asked to sign them.
She told RTE Radio she had tried to contact her brother to urge him not to sign his.
Junior minister Mr Costello said the likelihood of the siblings being released was "up in the air".
He confirmed that an Irish diplomat would accompany lawyers at the prosecutor's office, and the siblings would appear together in person.
"We know their welfare is fine, but we don't know at this point in time what the attitude of the authorities is going to be towards them," Mr Costello said.
Mr Costello said the siblings will either be released today or charged and have their detention extended.
"This is the first time that they are coming before the legal process," Mr Costello said.
"They have been detained without charge up until now. Two weeks have gone by. So this hearing will determine what will happen to them - whether or not the authorities will look for an extension and whether or not charges will be put against them."
He said the authorities had to bring the Halawas before a prosecutor today, because they are approaching their 15th day in detention, upon which they must either be released or charged.
"They have the holy day of rest tomorrow so the authorities have to do something today," he said.
"It could be an extension of time, it could be a charge, it could be that they are dropping all charges against them and they will be released and free to come home. It's not clear what it's going to be but whatever it is, it will happen today."
Chairman of the committee on foreign affairs and trade, Pat Breen, revealed that he was briefed this week on the family's plight by Ahmed Mostafa, charge d'Affaires at the Embassy of Egypt.
"The Charge said they were being well-treated, that the Embassy of Ireland had consular access to them, and that they were receiving family visits," said Mr Breen.
"He said it was for the justice system to decide the way forward."
Mr Breen said he hoped for the early return of the siblings and had deep concerns at the bloodshed that had taken place and over the difficulties that this was likely to cause for a return to a working democratic system.
"I stressed the importance of restoring constitutional government and adherence to the principles of human rights in the treatment of detainees," Mr Breen said.
He revealed that the Charge told him the Muslim Brotherhood had declined every offer to enter into the new reality that existed in Egypt, and that the situation in Raba al Adwiya Square and the Raba 'a Mosque, and in particular the presence there of firearms, and the increasing involvement of fundamentalist groups, gave the authorities no option but to take action.
"He said the future of President Morsi and other detainees would be determined by the courts," Mr Breen added.