All three points make a great deal of sense, although I sorta disagree on part of the first. When I went through the whole Geddoe Loses His Rune Ohnoes scene, Luc says it's a technique he learned from his mentor, and Sarah apparently has odd powers in general, so I'm not sure they'd need black runes and I think they'd avoid it if at all possible. ^^; Especially since Luc's well aware of what they do. Albert, on the other hand, I can completely see with one. He's the one who summoned Yuber after all, and I agree on the point of him summoning the monster.

As for the second, yeah, I highly doubt Leon would be so attentive to his nephew and not his own son. I think it was simply a matter of them saying "Ohshits we need more Silverbergs and Mathiu and Odessa are too dead to make any. DX"