MB4 258a: Mavui with Jews and Gentiles (390:1-2); Bitul Reshus for a Mavui (391:1)

A mavui where on one side is a gentile house and on the other side is 2 Jewish houses only one of which opens into the mavui (the other one opens into Reshut HaRabim). If the two Jewish houses have a window in between them can they make an eruv via the window?

If the members of a chatzer forgot to participate in a shituf mavuyot they can be mevatel their reshut (or vice-versa) so everyone else can carry (otherwise they ruin the shituf).