I honestly dont agree.

If my mom was raised by two women, and she decided to use the lesbian figurines despite marrying a man due to a personal significance it has for her.. I would not expect her let me dress her parents' figurine as men. In fact I'd think it would be pretty tasteless to alter it. I'd either suck it up and have a lesbian couple on the cake (which would be kind of weird), or I'd refuse to place it out of respect.

Realistically, I'd probably try to incorporate it on the came but not be the main focus. Or I'd just say fuck it and put a lesbian couple on my cake to mess with people. But I would not demand my mom to alter her adoptive parents figurine for me.