Spinning control arm bolts

I'm trying to replace the 3 bolts the hold the front lower control arm on the subframe of SWMBO's 2001 Santa Fe. They should have come right out, but they're spinning in place. The front 2 bolts thread into the subframe and go into blind nuts on the inside. There is no way to access these. The rear bolt is accessible. I can put my fingers on the top of the welded nut. Its spins.

I was doing it by hand. I switched to an impact. No joy. I put a pry bar on the end of the accessible bolt to put pressure on it to force it out. No joy. Is there something I'm overlooking? Pretty sure the welds have busted inside. Am I screwed?

Gonna have to cut the sheetmetal apart and reweld the nut or cut it out and replace.  You are screwed.  

Another route could be to source a new subframe.

Can you cut a small hole with a holesaw to get a socket on the nut? 

Yup, I'm screwed. One is definitely spinning. Already started cutting it open. I will eat a bag of dicks before I tackle a new subframe, though. 

Thanks for confirming my suspicions. 

You said you can feel the nut in the subframe.  Is said hole large enough to get the bolt through, if you cut the head off?

Or make the hole big enough to get a combination wrench on the nut inside?  Or some vice grips?

If you were to Drill a 1/2" hole in the Opposet side of each Bolt could you get something On it to hold it Still, an extension and swivel If it were a Nut.

Hyundai did some weird E36 M3. The nuts were square farmer nuts captured by what I might describe as a square cup. the nut was loose enough to account for manufacturing tolerances when the factory bolts, halving pointed tips, bullseye the holes. I think who ever put on that replacement arm over-torqued them, egging out the cups. When I tried to back out the bolts they spun and it was all over. I should have the thing buttoned up tomorrow, and have someone tack the new nuts in place and weld a plate over the hole.