You will get good advice here on AAM, if you provide some more information.
In general terms:
How much is outstanding on the loan?
What is the value of the house?
Does the relative intend to pay off the loan in full?
Is this intended to be a gift, or a full or part purchase of the house?
What is the relationship of the relative abroad to your parents?
Is the relative tax resident outside Ireland and is this ever likely to change?
There are ways of doing this in a tax-efficient way for all concerned but in order to get good advice here you would need to share some information.
If you don’t want to share the information your parents’ first port of call should be a solicitor who deals in stuff like probate and house purchase.