I know sounds stupid, but I snapped 2 bolts taking out the passenger side seat. I'm using a 15mm socket/ratchet combo for the 2 rear bolts, and a 15mm wrench for the 2 front nuts.
I tried to remove a rear bolt on the drivers side, and it didn't feel good; felt like it was going to give again.
This is one of those unfortunate situations where you may have to deal with a small amount of interior damage. I hit the bottoms of the bolts from underneath with some PB Blaster, let them soak for about an hour, and then used a mini-impact to break them free. On my Maverick, we had to blast the heads on the inside, and the interior still wreaks of that crap.
im sort of apprehensive on using PB Blaster on the inside of the car for that very reason. no access to air tools, let alone an impact gun. i got to make some calls and borrow a friends drill to I can remove those sumbitch bolts
See if the studs are still sticking through the bottom on the broken ones. You might be able to get some vice grips on them, or some stripped nut removers. They stick out quite a bit on my car. I know some subframe connectors even bolt onto them. Just PB Blast the bottoms of the bolts. It worked well enough for me. If you can't get to an impact, then give the bolt a couple quick smacks on the head with a hammer first.