I like this :
a. You must vote each day, but you cannot vote for No One. The first night you fail to vote you will turn your vote over to a randomly chosen member of a rival mafia family or an innocent and it will double their vote that night (I will PM the person who's vote was doubled so they know). If you fail to vote a second night you will die an untimely death.
3 per team does seem logical but with there being 3 mafia teams, *(noods quickly does the math - counts on her fingers and is thankful that it does not require the toes too! )*:....that means 9 total that need to be dealt with..... going to be an uphill battle, but should make for a good game.