User blog comment:Master Sima Yi/Assassinews 12-05-'15 — Assassin's Creed: Syndicate has been revealed!/@comment-26314858-20150709063110/@comment-13471981-20150711103915

So from what I've gathered, Henry and Arbaaz's relation was announced at an expo in Montreal. However, on a french Syndicate stream, Henry is referred to as Arbaaz's adopted son. So, Henry isn't Arbaaz's biological son, but he did grow up with Arbaaz as his foster father basically.

Yeah, Otso Berg is confirmed to return, but whether that's in Syndicate or one of the comics that's going to be coming out, who knows? There's certainly two "series" (I think) of comics, with one focusing on the Assassins, and the other on the Templars. I might be wrong though ^^;