Hi Miss
All male cats are called 'Tom' Cats, and all female cats are called 'She' cats. So you have two tom cats and they should both have nipplies. Both sexes have nipples just like we do.
It is not disturbing behaviour. It is simply that they have reached sexual maturity and want to mate. They will try to hump each other and will become aggressive. This normal behaviour in tomcats that have not been neutered. The normal age to neuter a tomcat is six months old. You need to get this done as soon as possible. Otherwise this behaviour will continue, and get worse.
So off to the vets with you!