to clarify its illegal to give anyone more than $10,000 without reporting it to the IRS. You can give someone $1 Million dollars as long as you tell the IRS and they pay income tax on it.
You can give you daughter $10K, You SIL $10K and $10K per grandchild without being subject to the income tax.
As far as OP’s problem, there might be a way to loan the money with every year an amount forgiven say 10% a year for 10 years then after 10 years the loan is forgiven and its likely the marriage is stronger.