Just because cats are litter mates does not mean they actually LIKE each other. And cats that live together may not even like each other (just ask Logan). So it does not surprise me that they are not together.
They WILL swipe at and attack your cats at this stage. I suggest NO contact until they are at least settled down themselves. And be prepared, this may take a while.
Good luck. What are their names (I don't think you said).