There was a doc style show on Phelps/his church etc a few years ago and one of Phelps children (can't remember if it was a son or daughter) and their spouse were talking in this particular segment. The "will anyone pick up and continue with Fred's mantle." question came up and both Phelps child and their spouse said they would. As they felt it was what God has called them to do, intended them to do or something like that.
This was well before legalizing gay marriage was on the forefront of our country's major issues like it is now. Whether that increases or decreases their resolve to carry on I can't call it. They also struck me as more militant than Phelps himself was.
Yeah, it's probably an acorn not falling far from the tree type situation (although I thought I read somewhere that one of his kids is estranged and thinks he's a nut). A good refutation for the 'speculation' that Phelps is Gov funded is that alot of those protesters (not sure how many) are his kids/grandkids - which makes sense because it's hard to figure he'd have many 'followers' otherwise. Nothing breeds crazy like crazy.