Do i have to go to Sil’s pretend ceremony?

Okay so for background, my husband and I have a horrible relationship with his parents for a damn good reason. But other than some trash-mouthing SIL did about us when we were newlyweds and she was a teen (probably influenced by MIL) we have an ok relationship. We aren’t close. We live 600 miles away (military) and we really just send happy birthday texts back and forth aside from her saying two sentences when we/they visit. I think it’s safe to say her and I are both introverted around people we aren’t extremely close with.
So surrounding her wedding, she’s been engaged to the guy (who happened to be my husband’s high school bestfriend) since she was 17, but living with him since she was 14. She’ll be 21 at the time of the ceremony, so they’ve been together for a very long time. It’s not like the ceremony really signifies anything special anymore because she’s pregnant & they’re planning a courthouse wedding next month. She originally set her ceremony date for June of next year. She is due in May and has adamantly refused to change the date, swearing she will still be able to fully enjoy her photos and reception. (Ah, to be first-time-mom naive again.) Anyways, I am due with our 3rd child in January (which she knew before setting her date, & before she decided to actively try to get pregnant-mind you her an fiancé just had a major breakup from Jan-April) Of course, hubs is best man. No worries no issues, of course I’m supportive of him being there. But she never asked us if the kids could be in the wedding, just told me they’d be ring bearer & flower girl. They will only be ages 2 & 1, which as their mom I can tell you is WAY TOO YOUNG. And I’ll also have to tote my 5month old & my postpartum x3 body along. She invited me to be a bridesmaid, I politely declined.
Who is going to wrangle 3 babies in wedding garb under 2 in a bridesmaid’s gown while my husband is being held hostage in a church basement doing shots?? If that weren’t enough stress alone, my oldest son has a very high functioning case of Aspergers... and then there’s my in laws who can’t respect his diagnosis or our boundaries as parents, add to the fact all of the awful things they have done and said in attempt to breakup our marriage.
So to begin with, this isn’t a trip we’re really interested in destroying our sanity for, other than the fact that my hubs and his sister are close and I would never want him to miss it because of us. But then you have finances. My hubs is E4, I am a SAHM because my career barely covered the kids daycare costs (it was literally a $20 take home per month for me to work so we decided to opt out of the stress) After we calculated travel fuel, hotel costs (there is no-one we can stay with that will not either drive us crazy to ends of hell, are genuine hoarders, or doesn’t have dogs- which my daughter and I are highly allergic to their dander) food costs (his family doesn’t cook- seriously, they eat Denny’s and Wendy’s and domino’s and McDonald’s and cereal and Debbie cakes and that’s about it.) wedding gifts, her baby gift, tux rental, bachelor night money, ring bearer outfit, flower girl outfit, etc. We discovered it would cost us over $2k to attend the wedding. (And all of the patience on the earth to pack 3 kids in car seats into his truck & drive 11 hours one way, try to pump breastmilk in the truck, stop every hour to change diapers, potty etc.)
Now, as people who live nearly paycheck to paycheck and can hardly afford big birthday and Christmas presents for our own kids or vacations for ourselves, that just seems ludicrous to me that we would take $2k worth of opportunities & privileges away from our own children to give to her when she’s doing just fine, and the entire visit will just be a dog and pony show of misery for me and the kids. (We are paycheck to paycheck for several reasons, most being debts my husbands parents got him into as a teen and the fact that we didn’t have anyone to set us up financially. We started with nothing but debts and we are finally almost free aside from our mortgage. Thank you Dave Ramsey. Lol)
I think between the fact that SIL will already actually be married, the impending mil drama, our finances, and the fact that my kids and I deserve rest & peace at their ages, it would be best for my husband to go alone. He can fly free because of his job, he can stay with his family (and is happy to), and he will be able to afford to eat just himself, enjoy the bachelor evening without feeling guilty for ditching me and the kids in a hotel, we can send a decent gift. And we get to avoid the kids being put in meltdown situations that not only could “ruin” the wedding; but cause significant harm to their self confidence too with adults who don’t understand their conditions constantly scolding them when I turn to attend another child. (like they do during our visits)
To send just hubs would probably cost around $500, which is much more “doable” for us financially, as we were hoping after paying off two final debts next year with our taxes to actually have some savings in the account. Does anyone see a problem with us choosing to do that? My husband is entirely on-board, he is tired of being put in the middle of the drama by his mother & we’re both exhausted of the financial stress.
Truthfully, I think our lack of presence will be better for all involved, SIL too. (she has 4 other ring bearers & another flower girl- so she isn’t missing anything) And there are things we need to put that money towards at home, we need a new roof, a storage shed, some basic home things we just haven’t had the money to buy (currently at the top of our list is a dining room table, a ladder, and a new washing machine- and for the record, we are super thrifty, most of our furniture, baby gear, tools, appliances & toys have all came from thrift stores or Facebook market. I haven’t had new clothes since I was single & debt free, we eat out maybe twice a month, used a babysitter twice since we had kids, and all of our kitchen stuff & almost all our decorations came from my childhood home that I boxed up and hid from the auctioneer at age 16 when my mom died-I never got anything else from my parents’ estate.)
I have no doubts I will be thrown under the bus and dragged multiple times for staying home and “keeping all of her babies from her” by my mil, (insert eyeroll and 3 year long story) I just don’t want to completely destroy our relationship with everyone else in the extended family. Thoughts if you were in their shoes? None of these details are a secret to them, so I’d hope they could be understanding.