Acting out or serious issues?

I am Vee, 25 years old in the United States

I have 2 cats Malibu (3yrs old, female) and a Smokey (9months old, female) and they get along pretty well. My bf and I moved in with a friend and he has 2 cats (both about 3yrs old, both male). At first they all got along and could be around each other with no issues, after a few months Malibu and one of the male cats started to just hate each other. they could be on opposite sides of the room and Malibu will hiss at him, or he will just slowly start getting closer so we had to keep them separate, we tried to slowly keep the door open and monitor them but they always end up fighting. Within the last month or so Malibu has been peeing on our clothes (she has her own litter box and we keep it clean) and been throwing up. I've looked it up and it could be due to stress and anxiety but with keep the cats separate we thought it would stop. I don't want to keep her in our room, we have a decently big house and want her to be able to roam but we are tired of breaking up cat fights. Is this something I need to bring her to the vet for or is there a way we can help them get along? I'm at a loss and it's been stressful not just to her but to us as well.