Family trip with in laws/ husband advice

I just need some other opinions to help me get my head straight so sorry for it being a bit longer. A little backstory is my husband and I have been together for 9 years, married for 1 year and have twins that are 8 months old. I’ve always had a pretty great relationship with my in laws I felt like until something changed when I got pregnant with my twins. I felt like MIL was more distant and back and forth with me(there’s a multitude of reasons and examples why it’s just way too many to type here). Our family went through a huge change last year with the loss of my FIL which I thought was a valid reason why with it being an emotional time for her. During my pregnancy and postpartum it’s still just made me feel like I’m just there and not really involved or looked at the same like my SIL’s fiancée who has been involved in the family equally as long as I have if not quite as long. Now that I am 8 months pp, I’m still struggling with PPD and PPA. I get overwhelmed easily, can’t sleep most nights despite the kids sleeping through the night, can’t take care of myself like I used to and so forth. It’s getting better at times but then it feels like I slip right back. Everyone’s wanting to go on a 14 hour trip one way with me, my husband, our two kids, MIL, SIL #1 and her fiancée, SIL #2 and her boyfriend, BIL, and our 8 nieces and nephews staying in the same place. That’s 18 people in one home for a week or a little longer. Mentally I just can’t fathom taking this trip that my husband is bound and determined to go on. I don’t feel as comfortable as I used to due to these things that have been going on with MIL and I’ve told him from the get go back in the beginning of the year I don’t want to go and instead of talking to me about it, he told everyone we’re going. I just can’t stand the thought of driving that far one way starting and stopping again with two babies that long in a car and being completely overridden and overstimulated for a week straight and having a mental breakdown. I feel like my husband isn’t listening to me and he gets super defensive any time I say I don’t want to go and doesn’t even attempt to understand where I’m coming from and instead says it’s just because I don’t want to be around his family. I told him before he’s welcome to go if I don’t but then he’s stated he’s going to take our twins with him(yes I’m aware he’s their dad and is fully in every right to do so just like I am but I’m just saying this for context). I don’t really know what to do. I just feel completely overwhelmed and burnt out and tired. I just feel like I’m not being heard and wanted to hear of any advice on how to go about having this conversation and putting my foot down or seeing if anyone thinks I’m being unreasonable. Mentally I’m so beyond checked out that I just can’t take arguing with anyone right now. Thank you for any input/ advice if you have any. And btw, for some that may think it’s an easier situation than it seems, for some people it isn’t as easy and that’s how I feel right now. So please just have a little understanding if you were in my shoes.