44 days out - venue ruined

Me and my SO are 44 days out and we are having MAJOR problems with his mother.
1) she went and invited 100 extra people in less than 2 minutes via her Facebook friends list.
2) she lied to us about the venue. So there’s is this hall in the same building as her daycare. We talked to the owners and made and agreement we could use it for the weekend if our wedding- free or charge. Sounds amazing right? Well They were suppose to do a little remodeling. I’ve been asking her and asking and asking how it’s going, and each time she lets me know it’s going beautifully. Major changes. Looks great. Well today she let slip that the remodel hasn’t actually started and they “probably won’t start before the wedding”. PROBABLY?! So I end up calling the owners of the hall and guess what? They’ve already started on ceiling and have removed all the tiles and have no intention of putting them back up. Now I would put them up myself, but I’m healing from a foot injury. My fiancé has a terrible back problem so he can’t do it either. Plus it would have to be done the day before the wedding. And what if we break one tile? There’s gonna be a hole in the ceiling.
So my problem is: SO’s mother is throwing a fit because she wants us to use the hall without a proper ceiling because it’s free. She told my mother “well if your daughter wants to go spend thousands if dollars on a local venue- go ahead” which I thought was rude. It’s too late to find another venue anyways, I tried. We’ve invited 300ish people, 250 which are planning on showing. A lot of those are children and I don’t believe it is safe to have them around open wiring and building tools.
Her whole family is saying I’m “overreacting”. I’m not dirt poor. I can find another venue and found some nice elopement -how my fiancé and I wanted to marry- in a local city.
How do you all suggest I go about this situation? Cancel the reception, elope, and plan a new one in a while? Im recovering from surgery and can’t/won’t be able to dance anyway. I’m actually in a knee scooter for 5 more weeks.
I know if I cancel the reception and wedding his entire family will have a MAJOR fit. I don’t think I will ever live it down. But at the same time- I think getting married in a venue without ceiling times and wires hanging down is rather embarrassing and trashy! Imagine the pictures!