Your parents can give you a present up to €332k and it will not be subject to CAT.
So if they give you an interest free loan, for example, then there would be no CAT either.
If you pay them interest, they will pay tax on it at their marginal rate. You will get TRS on it, I think, although I am not sure how it works.
It's a good idea to do it interest free. Your parents would be paying tax on the interest anyway, so it's not much of a sacrifice to them.
Giving you the money, might be safer than putting in the bank. Or put it another way, if you don't give it back, at least you will be benefiting from it. If a bank goes bust, your parents won't get any satisfaction of knowing that their deposit went to a good cause.
As stairs says, make sure that all siblings are involved in the process.
A solicitor should be able to draw up a legally binding mortgage agreement.
I know it's a horrible thing to raise, but you must work out what happens if you split up from your wife before the mortgage is paid off. There are many rows reported on askaboutmoney where the spouse claimed that the money provided by the other's parents was a gift.
Brendan