It's amazing that you've been able to have conversations about this with both your parents and they sound so supportive. You've done awesome so far.
Not that I have much experience with this (tho I did once have a convo with my parents about raising a kid with my partner and her other partner... before that relationship ended) but here's a couple tidbits...
Sounds like there are way more variables than I could figure out how to prepare for. So maybe a few exit strategies planned and prepared, so that if things get really hard, you can get out, or take a break and let people digest.
Re-confirm with yourself and partners who gets to call an exit, and who's uncomfortableness matters, and how much. Ie. if your uncle gets all quiet and nose wrinkly... Is that something you can let go of there?
Well some thots at least. Likely some other smart ppl on here... My first day.