I agree on the comments above. You have all the right as their mom to tell them what you feel about what they are doing. Talk lightly as a family and maybe just come out of their shells as grownups too? That’ll be something. If you really want to, you can either do that or a one-on-one talk to each would also be good. Communicating with family members can sometimes be a mess. A lot of understanding and open-mindedness is the key to settle things like this. Good luck!

You're adult kids will have to choose to stop their behavior and you can't make them like each other - but you know that ;) However, you can give your two cents about the whole thing. I wonder what it would look like if you tell them "Look 50ish kids I don't appreciate this behavior, I'm sick about it. Some changes need to be made."

Being their Mom, feel free to step in and give guidelines on behavior to get to the task on hand. I had a parent pass recently which my siblings and I worked together quickly so we wouldn’t have to deal with each other more than necessary. We’re all different and live in 3 different States. If we can do it so can your kids.