Nelson can always loose the weight, I'm sure he will eventually. Fat is just excess weight - which seeing as he's a smaller hw isn't really relevant, it's only an issue if he's going to lhw.
Semtex has power, speed, and is also technically good. But most importantly he's British
Thiago is good - but having bounced off Fitch, I don't see him ever getting past the top guys in ww. I'd take Josh in the rematch.
Stefan is a lost cause - it's a bit late for learning... essentially everything. His striking is bad, his wrestling is bad, his subs are ok but he takes a lot of damage getting there - he's Eric Schafer at hw.