One of the bolts I could not wedge the nut to loosen and I stripped the head trying to get it out. Now, it looks like I'm going to have to resort to drilling out the bolt or get a small fine tooth saw blade and cut the head off so I can remove the rail.
The rails I did get off are now at the house so I can refinish and prepare them for reattaching to the deck. So far, things seem to be going well. Just need to get that one bolt out so I can get to work on the other handrail.
Considering the bolts are phillips head, I'm now considering the possibility of changing them to a hex head. I wonder if that might make it easier for removal in the future, if it was needed. Either way, as long as things get bedded down good in the first place, it should be good as it is. If I'm going to drill out or cut the one bolt off, I'll need to find a replacement anyway for that one.