The repairs can wait until after the party. Fixing shit doesn't get you cake -- parties do! Where are your priorites, man? It goes: Cake, family, country, deity (optional), celebrities, house, etc. Got it?

Chances are your other relatives are aware of Mom’s memory problems and they are just going along with whatever she says instead of arguing with a person with dementia. It’s pointless to argue with a person with dementia. So don’t assume they think you are a bad son because you took care of her needs to have a safe house to live in instead of attending her party. And if they are dumb enough not to be aware of the situation you shouldn’t worry what idiots think. While parties and feelings are nice, having a safe home to live in is really more important and you were a good son to repair Mom’s home. Unfortunately you can never predict what a person with memory issues is going to remember and what they are going to forget.

Unless they have financial issues, if they keep taking advantage of you for free house repairs, insist on getting paid. Otherwise, outright refuse. Your mom needs to be assessed by a doctor and possibly placed in long term care, if only to get away from your toxic family.