Wow, good effort on that!
you can boost or favorite, but I am – and I think you are probably – looking for something with more variety, like emoji responses, right?
Honestly, this is low down on my list. Yes, it would be great, but I have had enough trouble finding something that handles uploading videos ok. Emoji responses are not a mandatory thing for me.
Pixelfed is an interesting suggestion. It always feels like it's intended to be public. Were you thinking each user would have to configure default privacy settings? I can see how to restrict to followers but haven't yet found how to stop anyone being able to follow you. I think for me, if a new user has to set up the privacy settings to stop them posting everything public, that's probably not the right platform.
BTW there is PixelDroid as a dedicated Pixelfed app, but it's only on Fdroid.
I don't even care about encryption (except normal TLS). If the intent is that it's for sharing within the family, generally with people being able to see each others' stuff, and I also control the server, it doesn't seem that important.
Circles seems like it might fit much of what you're after. It's based on Matrix and is intended for this kind of use case, but I don't think it's mature enough to onboard everyone to just yet. Them having lost FUTO funding means it will also probably develop at a slower rate now that's it's back to volunteer time (with the main devs likely losing enthusiasm after having that funding cut).