Messaging 6.50.42 sends to non recipients

[jdirt]

Hey Guys, good to be back. I have an old Samsung Galaxy S5 with a "Messages" app
v 1.0.0. The phone is running Marshmallow 6..01. Thats all I ever needed.

Then I got the LG V20. Now every time I send a message to brother A, my brother B gets the message too because they were both on a group message I created one time. I have tried editing the recipients and deleting recipients. I have even tried creating a totally new thread message but brother B still gets the message. Getting either brother to leave the group message would be impossible. They don't take instruction. And that may not be the problem. But no matter what I do, both brothers get the message. This could be very bad. So I m afraid to make any more group messages because I may never be able to separate them again.

On the G5, I can text messages to groups all day long and then send another message to only one person who is in the group message and this never happens.

How can I find out who made the message app in the G5 so i can get it in the LG. Or how do I fix this problem.
thanks so much