Can a Demon Weapon also be a Weapon Meister? So I just started watching Soul Eater and have the basics pretty much and u was wandering. Could a Demon Weapon also be a weapon meister? This got me thinking when watching the Thompson Sisters defend themselves against an army of mummies can someone shed some light on this? I know the sisters are just weapons belonging to Death the Kid.
The Weapon ability in Soul Eater is basically determined at birth. You either can transform into a weapon or you can't. There's no confusion about that. But the Meisters are a bit different. 

To be a Meister basically means to be able to perform well in pair with a Weapon. Not everybody can do that, but even among the Meisters, not all of them can perform well enough to be considered a serious threat or a great combo. You could say that a successful combo can do the Soul Resonance thing and unleash their full battle potential. And it doesn't really matter if there's more than one Weapon in a combo or no Meisters (non-Weapon) at all. Thompson sisters show that they can do just fine both in the role of a Meister and a Weapon.

So all members of a combo can be Weapons, but the Soul Resonance best occurs when there is a specialist non-Weapon Meister in it. At least that's what can be concluded from the series.