I would recommend a wash to remove as much dirt and feaces as possible. If the feathers are clinging to each other, depending how bad, dirty, close to their skin it can cause issues such as fly strike, irritation to the skin, restrict full range of movement and irritation.
Depending on your weather, a wash down with a hose and use your fingers/hands to scrub away as much as possible, a good dry off and either a warm sunny spot with clean bedding/flooring or inside till they are dry.
They may not like you for it, but they will feel better for it.
Ps.... I think with a clean up they are going to be beautiful looking girls!