Unsure how to tell my coughing cousin to not visit

I guess I need to vent a little about weird living arrangement and the fact that my cousin's bub and husband who has been coughing for nearly a week without improvement, and I'm getting slightly infected when visiting. I'm 39W, immunocompromised. So my parents from overseas came to visit and decided to live in cousin A's house who is conveniently close to shops etc and no stair. My house has stairs, so we decided it's best mum who can't go up and down stairs to stay at cousin A's home. So I have another cousin B, she lives somewhere else but because she knows my mum is visiting, she decided to sleep over at cousin's B, together with her husbsnd and a 8month bub, who I just learnt had persistent cough from last week. I thought nothing of it, but I visited them twice (since my parents stay together now with them), and everytime after the visit my throat gets congested. Anyway, I'm kind of scared of the cough and unable to tell her that maybe it's best if she doesn't sleepover at cousin's A until her family stop coughing? But I know I can't just do that. Cousin A is pretty welcoming to cousin B to stay over. It's just really me, who's having a bit of problem with the cough. At the same time I might have low key jealousy that she's just trying to get closer to my parents (as my dad likes to organise drinking party with his husband, who drinks alcohol a lot.). I tried not to think to much of it but is it too far to ask my parents along with anyone who lives with cousin B, not to visit, until cousin B's bub and husband stop coughing?