I couldn't resist adding to this one.
Honestly, I wonder if ANYONE likes Heath. He's too... Broken for me, in a sense. I just can't stand his "woe-is-me" attitude.
Markus is my personal favorite, I don't even mind being asexual (I'm demi, after all).
However, I do empathize with Randal a great deal (and I'm a sucker for things getting rough).
Anyway, after playing all of the routes (again):
1. I think that crying phone call is from either Heath or Markus, especially since you can call Randal right after and he sounds normal.
Heath for obvious reasons-- He's not the current love interest.
Markus because he admits in his own route that as soon as he saw the MC, he saw their entire relationship before his eyes.
The most likely is it being Heath.
2. I'd have to play as other Houses (or the prequel) to tell, but playing as a Gol you see a halo on his head that changes the further into his route you go. I don't remember if you see the glowing eyes in other Houses, either. If so then I'd say likely a Gol, yes.
I do like that theory that he's a cross, but I'd say a Gol/Mavvar cross instead.
3. He's basically a stand-in for Jesus, so stigmata makes sense.
He wants to peacefully bring the Houses together but his group is too rowdy. Like, Markus mentions, the Crusades. The majority of conflicts all over the world have been fought in the name of religion.
Honestly, these guys live in America... Why can't they just have a three-way presidency with representatives from all three Houses as Congress and vote on the rules they come up with? It's at least better than a dictatorship.