To answer the first, probably not. Or rather, you may be able to get it to fit with a lot of blood, sweat, toil and tears. Probably easier to make one yourself. There's the Clothing Convertor from DAZ but I have no idea how well it works. I have a suspicion that a straitjacket may just be beyond it, though. OTOH, if M3 is mostly going to be hidden inside it, perhaps it wouldn't be too much of a problem to hide the chest and arms, and just parent the jacket to M3. Second question - export the whole of them as one OBJ. Even if they aren't physically touching, they will load and move together if you do that.

Coppula eam se non posit acceptera jocularum.

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