I took the phones of my parents and siblings to install Telegram on them myself ;) My brother and sister use it sporadically, but I still can send them messages knowing they will read them sooner or later. My parents are more proficient with it than me, now :).
If my kid or sibling took my phone and install ANYTHING on them, i would wipe reset the phone and never trust them ever again.
I'm sorry to hear that.
Yeah, do not touch my phone and do not install apps on it.
Sounds like you don't trust them already.
This was always the problem. Your social media environment and opsec too relies largely on your social graph that you have no control over. Maybe LLM based scraping/automation solve this mid-long term?