A relative’s past generosity does not settle every present disagreement.

Debt and authority are different things, though families often let one stand in for the other. Someone who helped with a deposit, took you in for a year or looked after your children has earned real gratitude, and gratitude does not convert into the final word on your choices now. When old kindness is invoked to end an argument, both the kindness and the argument get damaged. You can be thankful and still disagree.

If this comes up, thank them sincerely for the past and keep it separate from the present question. Say both parts in the same conversation, so neither one is being denied.