TandemGeek

If a good soaking with penetrating oil before using plus the new tool doesn't give you enough leverage or if the new tool won't stay seated, you should be able to 'carefully' use a pair of Channel Lock pliers to hold the lip of the female nut against the chain ring.

However, you'll want to put a small piece of metal, wood or plastic between the face of the chain ring and the pliers jaw flat to keep the pliers from maring the finish of your chain ring. Use a hardened steel allen wrench on the screw head. Worst case scenario, the bolt head's allen flats will strip-out, in which case you can either attempt to use an easy-out extractor or go back to the original Plan B: split or drill out the bolts. Frankly, I'd be surprised if the Channel Locks + steel allen head would not work but, again, until I can see just how mangled the bolts are all bets are off.

As for determing if the chain ring or crank arm bolt holes were deformed, just check them against the stoker's timing crank and chain ring holes. Your new chain ring bolts should fit up with the same amount of tolerance; there's typically some play. If the new bolts can be torqued-up and create a firm press fit with the cranks, even if the holes are a little deformed, you should still be OK using the old cranks and rings. However, you'll need to spend some time making sure that you get the ring centered so there aren't any excessive high or low tension points in your sync chain as you rotate the cranks. If you find that while riding the chain rings shift off-center, you may need to revisit the crank arm and/or chain ring replacement scenario.

As for how common this is, as noted in another recent thread on chain ring bolts coming loose we've had it happen a few times, but not where near to the extent that you've just described. It typically happens when new chain rings, bolts or new cranksets are installed and you neglect to check the bolt torque after the first couple rides. Now, if chain ring bolts come loose you'll typically hear a clicking noise that stays in sync with the rotation of the cranks as the chain ring deflects away from the crank arm under load on each turn of the cranks: that's your first clue that something's not right. This can sometimes be mistaken for a bottom bracket creak. Again, the solution is to always recheck chain ring bolts after a recent installation and/or to chase down any unusual noises that come from your tandem, as those are usually precursors to bigger issues down the road if left uncorrected.