i am not in the EU. and even there, i probably would have. it's a group for all the parents so i don't see the problem there, and even if there wasn't such a group, the teachers could send pictures privately to each parent. but not per SMS.

Required communication

there is required communication, and there is convenient communication. convenient communication helps keep the mood more friendly. also, you didn't read, international SMS and calls are expensive. and i am travelling a lot. i am not reachable under my home number all of the time, so i would have to tell my landlord my new number every time it changes because i am in a different country. (forget roaming. the cost for that is atrocious)

matrix

i use matrix. the experience is horrible. at least if you are trying to use encrypted chat. half the time it breaks. the key management is way to complex for a normal person. i have a technical friend who switched to matrix because of me. he threw it away in disgust when our chat broke for the third time. he got me to switch to signal (which now fortunately allows me to hide my phonenumber, so it became an acceptable option.)

compared to IRC, xmpp/jabber and deltachat, matrix has the worst usability among FOSS tools. i don't have the patience for the amount of teaching i would have to do, especially as it would all have to be remote. i live on a different continent from the rest of my family.