First, to protect your mattress, you can buy those plastic liners. They are only plastic on one side. Places like Target and Kohl's and Sears sell them. You might want to check on that.

Catty1 has Oscar, she keeps a collar on him and sprays the feliway onto the cloth around the collar. Have you tried that? I'm sure she can explain it to you better.

Keep their claws clipped, to limit the amount of damage they can do to each other.

That's all I can think of just now.

Good luck.
Sandra