Actually, Juu's question and answer here, Weapons have limited use of each other. Example, Patti and Liz in Soul Eater have used their gun form to threatening people and shoot bullets, but nothing beyond that. And since everyone being kidnapped is a Weapon, overpowering them wouldn't be difficult. Also, if they're being properly contained (and I would assume as much since the kidnappers are going through all this effort), they're being monitored and locked up so they can't escape unless assisted out.