No squad can use the exact name another squad has, if I recall. You have to have at least 1 character different, right?
So if you want to avoid having folks think these newbies are yours, what if you just change the name slightly? Like put a * in front of and after the name? Or put "..." around it?
Just something that's the equivelant of Rob Schneider in "Judge Dredd" saying "Excuse me! We're not together!!"
As for getting them to change their name, I don't think you can do anything to force them.