MIL adopts cat even though she’s knows I’m deathly allergic, Help!

Ok so I’ve never done a Reddit post so just bare with me on this one. I just need some sort of advice and not feel like I’m crashing out. So to start my boyfriend and I and our 3 kiddos live with his parents, as well as my boyfriend’s brother. This was due to a multitude of reasons, but his parents invited us to live with them to help us more or less get more established and be able to afford a home versus renting. My boyfriend’s brother lives in the basement and all of us and the kiddos live upstairs. That being said the downstairs bathroom doesn’t work and will over flow due to the upflush not working.

So his brother and girlfriend come upstairs to obviously use the bathroom. With that being said, we have been living with his parents for around 3 years now. His parents have always had a rule of no pets cause of boyfriend’s dad being allergic, or allergy sensitive. So we always kept that in mind, as well as his mom being extra sensitive to “vanilla” scented things. And we didn’t want to over step or cause issues while living here. And do things that would trigger people, bare this ALL in mind. So you’re probably wondering what does this have to do with me? Well, mind you I’m highly allergic to cats, if I’m in the vicinity of a cat I have breathing difficulties, hives, puffy eyes the whole nine and even had to get a epi pen due to having severe allergic reactions and not being able to breath and being hospitalized at one point in time. This was all known by his parents and brother. Well needless to say my mother in law on our car ride to get my kids mentioned something about dropping me off at home later in the evening with the kids and going to his aunt and uncles to go out to dinner with her son and his girlfriend. And I felt a little slighted cause I asked why we were not invited as this is a common theme of us not being invited to family outings for various reasons and or just not keeping us in mind which I thought was weird. Just for her to say she is adopting a cat from his aunt and uncle, (because they foster kittens), and that it would be a basement cat. And that she wanted to keep it a surprise. And she knows im highly allergic to cats and didn’t want to take me in the car ride with her and the kids to get said cat.

At first I was dumbstruck and decided it was best to keep my mouth shut. And I think she noticed me get slightly flustered and tried to make every excuse in the book of how it will stay in the basement, even though dander and cat hair can be transferred from basement to upstairs and vice versa. Due to boyfriend’s brother coming up and downstairs to use bathroom as well doing his laundry (with cat hair) on his clothes in the same laundry that I use for my kids and myself. As well as it getting through the ventilation system throughout the house and causing me to have flare ups. In addition to his brother car pooling with me and his mom to work (cause they all work at the same place) and his car is not working on top of it and hasn’t been working for months hence why he car pools. Bear in mind, I have a (2 year old) that we are not even sure may have the same allergies as well to cats. That being said I have nothing against cats I think they are lovely I just unfortunately can’t be anywhere near a cat is at or I get deathly allergic and I’m more or less afraid of ending up in the hospital again. At this point I’m afraid to mention anything to his parents without coming across some sort of way cause we weren’t taken into consideration or even asked what we thought about having a house pet upon us being told no pets whatsoever. But as soon as boyfriend brother asks for a basement pet, it’s not a problem. I feel hurt and I feel as if they just don’t care and ultimately are trying to push us out in some sort of way. But this will ultimately cause problems, not only with me being allergic but also the fact that my middle child loves to hang out with my boyfriends brother and girlfriend in the basement and I’m afraid she will bring cat dander up with her though out the house.

And I don’t want to resort to her not being able to hang out with them in the basement around the cat because it’s not her fault that I’m allergic to them. But also I don’t want my kids to go ballistic and freak out cause they can’t go into the basement and hang out with their uncle, MIL has confirmed that every time my kids go into basement she will immediately shower and wash their clothes knowing I won’t be able to do it due to how highly allergic to cats I am. But I find this hard to believe as she already has a hard time even wanting to spend time with her grandkids and it’s always some sort of issue or problem to begin with, she also mentioned changing the air filters in the house, but how long will this last for before she stops caring and ultimately doesn’t do it. I know the best advice would be to move out but we are currently not in the spot to at this current moment, what do I do? And how do I not come across as a A double scribble and really be able to voice my frustrations? Mind you they are still picking up the cat tomorrow regardless of my boyfriend mentioning something to his parents, and they said if it causes issues they will take care of it, But that ultimately isn’t fair to the cat in the end especially if I do have a severe reaction and they have to rehome it. This all around sucks, and I’m at a lost of what to do. Please help.