Well start with lots and lots of penertrating fluid and giv it time, kep soaking things. Maybe some lcaol heat from a micro torch or hire an induction loop to get heat on the bolts, I guess they have been in there a very long time. I would try my impact wrench ona long extension using a universal joint too. It would probably damage or break the UJ but worth it. Or try a socket and bar and just keep tapping teh end and see if that will do the business. If the bolt is really rusted in this may need to be an engine out job when you could give the whole thing a fettle and get proper access and check everything.