They're supposed to come from England later this month and we were supposed to meet. I was convinced (and so was my BF) that they would come, sit a few hours and go about their adventures.
Well, yesterday my BIL texted me (why him and not my sister is beyond me) to check if we were okay with them staying the night... And for various reasons, we are not. Some of which I explained to him, although I had to go into much more detail than I was comfortable sharing until he said "Okay, I didn't know it was that bad". Which I thought was closing the conversation.
Not long after, my sister texts me with an innocent "do you have a minute?". I'm like, aha, here we go. He didn't succeed, so he sent you. Classic BIL.
So I start the conversation with her, it's the same story, then some added (I thought reasonable) disadvantages, but she said "we're okay with everything you said so if you don't want us there, you better make a better excuse".
At this point I'm calling my mom, crying, because I desperately don't want my BIL here for the night, and I just don't know how to handle the situation politely.
Their 4yo son is not the problem at all (despite my sister's best efforts to tell me he's the only problem for us, while also convincing me that our problem with him is non-existent). My third trimester is the problem, the July heatwave is the problem, my BF work and sleep schedule is the problem and also my pets are sort of a problem, with my second room NOT being a guest room but a nursery in progress. I am not comfortable dealing with all that stuff on top of having my BIL here for the whole fucking night, while I really have a deep issue with the guy. And I know it's just a "me problem", I acknowledge that. However, I have a problem and I am not in the slightest ready to share my scorching hot roof with him because I, a pregnant woman, will be uncomfortable. Not only because of his presence, but also because of the heat, of my probably sleep-deprived SO, the lack of privacy I desperately need, and because of my devilishly mischievous pets who love to mess things up whenever we have guests. I'm sorry if I seem to be a bitch because of it, I don't need and don't want that conscious and subconscious stress in my body right now.
And she dares to say to me that they're not trying to force us or be pushy about it. Then take the fucking hint! And why did you start the conversation when I just finished it with your husband? Why did he even text me first? You're my sister, I'd rather discuss it with you than him! I'd much rather have my SISTER ask me "hey, we're in kind of a predicament, the situation is xyz, do you think you could have my family for the night?" And it would still be a "no" for me, but at least I wouldn't feel attacked. It would help a ton if my "no" was taken as a complete sentence and not a negotiation.

At first she seemed to take it well with "I had no idea it was so stressful for you", "are you sure it's just that? Is it about BIL?". Well, it's about all the things I already told you that constitutes for our (your hosts) comfort and yes, a little bit about BIL. I'm just not okay with going through that stress at this time.
She's all nice about it and then hits me with "I just feel like you're maybe catastrophizing a little bit. Maybe try to think about it calmly and let me know tomorrow, okay?"
Excuse me, what?
Do you mean I'm catastrophizing about your husband? Yes, probably. I probably should reach out to my therapist about that. Truth be told, it's not on my current priority list, though.
Or do you mean to invalidate that our comfort is just as important as yours? Bitch, I'm done