If there's only two flats on the heads instead of a normal hex head, there are splines on the bolt under the head. You have to put the nuts on backward a few threads, then hammer the bolts out. They won't turn out.
Also look for a rubber insert behind the hub. Some GM models use that, and there will be a place to run in a bolt to hold that together while you have it apart. If you let that get away, you'll never get it back in again. That is a real frustrating design.