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"but what about xmpp?"
We did that for about 3 years before moving to Matrix. At the time, OMEMO support was quite rough, especially on iOS. And XEP support was hit/miss for various clients that people would install.
Every time I ask folks to switch to some new chat tech, I burn some serious "capital" with the family. So like, I gotta be 200% confident the new thing we switch to is better at meeting our requirements 
I managed to get my close family using #Matrix for communication, we have been using it for about 6yrs. For the most part, it has worked pretty well!
But the 2 biggest complaints I have are:
1) key mgmt is soooo hard for people who are "non-technical" to understand and do consistently. So many times someone got a new phone, traded in the old then couldn't read old messages on Matrix
2) Android matrix app notifications are totally busted for several folks. We can't rely on this for fast comm.
