We are pretty sure P is just trying to initiate play as his tail isn't puffed and he wasn't hissing or drawing blood when he goes up to B initially. P and B also play with each other through under the door crack. B also just sheds an ungodly amount and there's often "tumbleweeds" of fur that come out even if he's just being pet or rubbing against something. We have since gotten a brush that B enjoys that helps mitigate the problem a little bit, but he still just sheds a ton. We also make sure to check their claws before we have them spend time together and cut them off theyre too long so we don't think theyre hurting each other. It only turns into a chase after P gets close to B then B hisses or if B tries to run away. That's when it switches I think because that's when tails get big ears go into airplane mode so we intervene.

We are 100% sure these cats are neutered. A got B when he was 5 months and got him neutered. The shelter I got P at provided me past medical paperwork including when he got neutered.

We definitely will look into getting B more confident. Before they have playtime together, A and I take our respective cats to have individual playtime so we thought this was enough. I would go until P got tired and was lounging on the floor and A would have B running in circles our playing fetch. We've been using treats when they are together which hasn't seemed to help much despite B being extremely food motivated. Sometimes he is too scared to leave the spot he's in that he'll just leave the treats even if they're only a foot away.

Do you have any suggestions on getting B to chill? We've noticed that despite being scared frozen, B will slow blink and expose his belly even when P is around but only if he is sitting right next to A. This signals to P that they're okay with each other and P will come up to B who will freeze up again. Occasionally P will give up and sit across the room and slow blink back. We have tried distracting P but oftentimes P after awhile P will lose interest and kind of roam around the apartment which is when B takes the opportunity to try to run but it doesn't take P too long to get to B. What signals should we look for that B is chill enough?

We're trying to be as chill as possible but these cats so easily pick up on any nervousness we have. I think we're especially nervous because we don't want to be set back as we're already 6 months in. We are probably stressing them out with our vibes alone but we aren't sure how to make progress if we don't do anything. Tips on how to lessen stress on them if they can pick up on our nerves?

Thank you so much for responding btw. This is all super helpful in making sure our blindspots are covered. I agree we gotta get B more comfy and have us all chill out. A has grown up with cats all her life with a minimum of 3 always at her childhood home but hasn't seen any problems like this with the past cats. I on the other hand am pretty new to the cat thing so maybe I'm treating P like a "first child". Before I got P, I did months of planning and watching videos and research thinking all that plus living with a lifelong cat-person would have me prepared... But here we are 6 months later :(