Do you remember how Trafalgar Law can switch people’s minds/hearts/personalities?
During Punk Hazard, two Devil Fruit users lost their bodies to someone else: Chopper and Smoker. And while Franky and Tashigi had those bodies, they also had the ability to use the devil fruit powers.
Even when they were outside Law’s Room, they didn’t switch back, so it would last as long as Law wants it to, right?
Why doesn’t Law switch his weak crewmates’ personality with strong devil fruit users? He hit Smoker and Sanji with it, so it shouldn’t be TOO much of a “The enemy is too strong so it wouldn’t work” problem.
In this way, Law’s crewmates would get a body with a powerful devil fruit, and the enemies would get a weak body the crew can easily dispatch.
*Theory by Briaria