Never bother with your Roman allies. Don't bail them out. Hamper their expansion. Make their likely expansion cities prime targets and try to match their invasion with a Senate mission in a similar area.

In my Julii game, I had virtually crippled my Roman friends. The Brutii were stranded in Southern Italy (for some reason, I managed to beat them to Appolonia). The Scipii lost the race to Lilybaeum, and when I saw them hesitating to take Syracuse I took that as well. Basically I managed to confine all of my rival Romans to their initial cities. I believe I was absurdly lucky, particularly with the Brutii, but that's the way the cookie crumbled. I proceeded to continue with my stranded friends' conquests of Greece and Africa. Needless to say, within 10 turns I owned 3 major cities: Carthage, Syracuse, and Sparta.