I'd put Jon in Bran's place as hero A.

Essentially, Jon's storyline has him traveling North with his companions - many of whom have died one way or another. They don't necessarily have to be people who went with him knowingly to The Wall, just people whom he was close to in life - hence there is companionship.

His (cough) "father" Ned Stark is dead, Robb is dead, remaining family presumed dead; biological/R+L=J parents dead. His love, Ygritte, dead. His friends in the Night's Watch, if we are to view their fates in the show as a possibility for the future books, would end up dead.

Jon already knows The Others are coming and thus The North needs to be united/guarded.

Meanwhile, Hero B, the one who is adept at negotiations, would be none other than Tyrion.

Jon and Tyrion have already had an interaction in the book/show, so there's a slight affinity there. It's possible that Tyrion will believe Jon's tale of what lies beyond The Wall.

Mother Rhoyne's "children" can essentially be:

• the dragons, as the show presented, Tyrion was able to calm their aggression, very possible that this happens in the books
• Jon and Dany, given their direct descent from rulers of Rhoynar; the scenario being that Dany has already made her way to Westeros, intent on domination, while Jon is protecting The North and will not yield; Tyrion essentially stops Dany from further spilling blood on Westeros in order to prep the populace for War with The Others
• Westeros in general, ie. "those alive at this point in time, everyone, are Mother Rhoyne's children"; basically same as above but this time Tyrion's diplomatic skill is able to unite the entire populace against evil

Hero C remains Dany.

I'll propose another alternative theory as a reply.