It's great that you have a supportive principal, even though it may seem like he isn't doing anything in the way of getting these three sticks off your back, when you talk about veteran teachers i guess there's not much you can do this way. Keep on doing what you are doing and it will definitely show these three that they can't get you down and that they just can't always get their own way. It's hard to not want to smash something when someone is talking trash behind your back. I can imagine you're frustrated because you can't really come right out and like start a fist fight or swear at them. You can't make them admit that working cooperatively in a department makes everyone happier and that cooperation sometimes means compromise.
Some people just think they're too good to do their part.