Is the cage plastic? Is it possible to fit it in the bath?
You can wash it with hot water and either washing up liquid or a cage cleaning spray, I recommend Bob Martin's My Little Friend cage disinfectant. It's very good and it kills all sorts of stuff.
You can wash most fleece in the washing machine at 60 degrees with non bio washing powder and a little bit of vinegar. Dry in the sun and they will smell nice and fresh. The hot water will kill any germs.
Plastic toys can be washed with hot soapy water, if my wooden ones need a wash I rinse them quickly in water and then I dry them in the sun. The sun also kills bacteria.
When my wooden hideys need a wash I wipe them with a damp cloth and then I dry them in the sun.
If you have to bathe your guinea pigs I recommend Gorgeous Guineas conditioning shampoos, they make their fur nice and shiny and they are gentle on their skin.
I wouldn't treat them with any medicines unless you think they have something but in that case a check up at the vets might be a good idea.
I don't believe in using medicines unless they are needed as they can be ineffective after a while.
I hope this helps!