Second fake death of Lucian, well here he really fakes it, but if you by the other fake death mean Div2: Ego Draconis, that can't be called fake death, when he was in fact imprisoned in another realm by Damian. That's hardly his own decision to pose as dead. I haven't been through Beyond Divinity yet, as the game doesn't work well on my computer, so can't say if there's something about Lucian's fake death, but since the whole story of that game takes place in another realm (Nemesis), I pretty much doubt it. There's also Divinity: Original Sin out there, but honestly I have absolutely no experience with that, I went straight for it's sequel.
Zandalor isn't explained, but he's some kind of Deus Ex Machina, he shows up, gives you clues and is off (in Divine Divinity and even more in Div2: ED). In D:OS2, you don't really need his help, there's plenty of other similar elements there (one would be Lohse's upstairs visitor, if you play as her, basically functions as Zandalor v. 2.0, I guess the other characters, including custom ones, probably have another gimmick, that works similarly, one of the Seven in the Hall of Echoes perhaps? Can't say for sure, I hardly remember my last progress with a custom character). Storywise, he might be on lookout for Damian's return (as he does indeed return in Div2:ED and there we have Zandalor again) and doesn't pay attention to what's going on in the area of Reaper's Coast. Though it's strange considering how much Sourcery happens there, that it attracts the Void, but not the mage supreme, that is Zandalor.
Arhu can help you with the main quest, although I'm not sure, if it's really needed, if it can be solved without his help, after all, he can even die in this game (but it's canon, that he survives, as he's shown in the ending of Flames of Vengeance in his cat form), you can then talk to his spirit to get the info you need, but he might be even completely missed, if you're not doing the Vault of Lord Kemm quest (I think the quest is optional). Guess there's still a way to go around that to get the amulet and the scroll. Not completely sure though.
General Alix as Alexandar's mother? I had absolutely no idea there was anything going between her and Lucian. Playing DD as a female character, I don't even see the possibility there. XD But well male Lucian is canon, so nevermind that. Makes me wonder, how old is Alexandar actually? He's an adult now, did he meet his "brother" at least once in his life, or was he born after Damian was gone? It's shame that Div2: ED doesn't mention Alexandar at all (does it? I didn't find anything, maybe just missed stuff about him, possibly).
Does Lucian wear Dragon Armor in any cutscene in DD, Is it canon, that he has it? Because as far as I remember, it was optional and not really needed for finishing the game. Sure it helped to wear it, but it wasn't part of the main quest. So that may be the reason.
