how to support my grandchildren?

I’m interested how you know of the situation if they have no social media, no phones, I must assume you are seeing them?

Have you offered to help them with school work online?

BBC Bitesize is brilliant. I whatsapp my grandchildren and we go through a lesson together. I am not a trained teacher so we go through it at the same pace. Usually half an hour is enough and they seem to appreciate it.

Oh yes, Lucca I went away and was still thinking about it...
So difficult. But I think the school should at least have support.

it sounds like they are being kept in an oppressive atmosphere.
could you contact child protective services.

I guess the 18 Year old will be able to leave the family home, but it’s hard for the 11 year old.

Op says kids “do great in school”

Just suddenly wondering if your daughter is home-educating too?

What a terrible controlling atmosphere. No words.

Is the 18 year old at school or college? I think you are USA from using "mom" - could you suggest (next time when appropriate) that he speaks to the school/college councillor? They are in a better place to support him as won't be cut off as you might be.

It may sound harsh, but it is really not up to you to ‘do’ anything, especially something which may well make matters worse. I’d say all you can do is provide a listening ear if you’re asked.