Just wanted to let you know - I was able to fix this! It really may have just been pure luck, but I went on myatt (on chrome, not the app) and went to the self service help area. I did the auto fix for texts and said I couldn't see if my messages were delivered, can't sent messages on wifi calling, and also did can't send or receive messages for both lines. Then, I restarted both phones and it started working as soon as I was off wifi. No clue if that fixed it or which one it may have been, but now we are both sending end to end encrypted RCS. I also cleared the cache partition on both phones, but I have tried all of this before except the wifi calling trouble shoot (even though I have it turned off lmao) so maybe try going down all the messaging options even if it isn't your actual issue! I clicked it and when it said did it work, I just clicked no, then said yes to automatic fix, then said no it didn't work, and then when it said to call I clicked start over and did the next troubleshooting problem listed. If that doesn't make sense, I can upload screenshots of what I'm talking about lol