46-year-old Sean McGrotty and his sons Mark, 12, and Evan, eight, were with Sean's mother-in-law, 57-year-old Ruth Daniels, and her 15-year-old daughter Jodie Lee when the vehicle slid off a slip way yesterday evening.
The incident, described by police as a tragic accident, happened in the small County Donegal town of Buncrana but the family came from the nearby city of Londonderry.
The only survivor was a four-month-old baby, Rionaghac-Ann, who was rescued by a bystander who swam out to the sinking car.
Mr McGrotty's wife, Louise, had been away on a hen weekend.
Father Paddy O'Kane from Holy Family Church in Londonderry said: "Words fail me to describe the depth of pain and the vastness of this tragedy."
"I am 43 years a priest and nothing compares to this. This is way beyond anything in my wildest imagination.
"This is the worst thing I have ever had."
Revd Knox Jones, a the local Presbyterian minister, told Premier's News Hour last night's tradegy is yet another blow for the town.
He said: We are shocked by the deaths and, unfortunately, there have been tragedies in recent years in Buncrana before this. This is yet another really severe and saddening incident in the town.
"With it being Easter week, there are extra services in most of our churches.
"I know, on Wednesday, a number of Presbyterian churches in the city, here in Londonderry, will be meeting and we certainly will be praying for the family."
Father Paddy O'Kane added: "When I went up [to the family home] this morning, people were just standing around. Men were just standing looking at the ground not knowing what to say.
"All you can do is just shake their hand and say 'I'm sorry'. A respectful silence is all I could muster.
"Before I left the house, I said the Lords Prayer with everyone to give Louise and her family strength.
"We all knew there was a terrible tragedy that happened in Buncrana last night but we didn't realise it was on our doorstep.
"People are very good in this parish and they will do all they can to help but what can you do and what can you say."