wtbh, I'm not really sure they (your ah and family) can do anything at all legally. Some texts were sent around, ownership may be unclear and the text messages weren't nice.
I really don't think this is anything to get worried about. It sounds juvenile and sophomoric, not something to be concerned about. If this were a legally liable situation just about every high school and college student in the country would need to be worried.
The are generating drama and you are responding. To nip this in the bud stop responding.
Your friend,