If it is truly a gift, no strings attached, I would take it.
I would also take a look into what the laws are in your state, just so you have piece of mind for yourself.
In Alberta, upon divorce, a gift from a third party is exempt property. As an example:
– House has $50,000 in equity;
– In-laws gifted their son $10,000
– House is in his name, but you are married.
He gets the first $10,000, and you each get $20,000. He ends up with $30,000, you end up with $20,000.
If the house was in joint names, by putting a gift from his parent into joint names he is deemed to have gifted half of that to the marriage, so he would get $5,000, and then you would each receive $22,500.
If you accept the gift, make sure you are aware of the consequences of how it is gifted (is it a gift to him or a gift to both of you?). You can evidence this by showing a gift letter, that shows the gift is meant for one party or both, or a cheque made out to one party or both.
There are a whole lot of other considerations if you sell that house etc. Sorry to put this in a frame of “if you separate” when buying a house is a very exciting step in your relationship. Obviously you aren’t worse off by accepting the gift, but I have had clients blindsided when they are told they don’t receive 50% of the equity because the other party’s parents paid the down payment, particularly when the gift from parents “freed up” other money, so they spent it on vacations etc. and they can’t get back the money they spent on Hawaii, but their ex partner is still getting his money.