Cleaning up very old oak and other hardwood roof beams
You have a pile of wood that needs to be turned back into lumber.

As they are to be structural, the beams should be resawn until there are no "rough bits" left. Digging the rot out of a beam makes that beam no thicker than its narrowest point; a weak link. The whole beam should be resawn to its narrowest dimension where there's rot. Effectively, that's how thick it is anyway.

Whatever tools you use should say nail embedded wood, or just use metal cutting blades. Sanding nail embedded wood just takes a lot of paper and patience. A quick once over with a standard grinding wheel might save you a lot of paper. Pull or set as many nails as possible.

What you're asking for, which I do not suggest, is probably (diamond) granite grinding wheels. They're liable to catch on a nail and make for a really bad day.

I would suggest trying a grinding bit for drills, a grindstone bit that will turn your drill into a gigantic Dremel tool. Again, make sure that what you're left with is acceptable structurally, at its narrowest point.

If you want to preserve that old look and not re-saw them, consider sand blasting them. IMO, re-sawing or blasting is the only way to really see what you're dealing with (without wasting a lot of time and paper), especially if they're as bad as you say they are. 

An expensive option is to have them professionally planed. I say professionally (expensive) because you would ruin yours, and they will charge you for a blade replacement on theirs, regardless of its condition afterwards.