Seriously, the curtains are really the least of your worries regarding germs and bacteria in the motorhome!!
There is a reason that ventilation, humidity, mold, and cleanliness are always mentioned in regards to all RVs. I wont even mention what happens on boats!
The only way to wash them, (if you're talking about the windshield privacy curtains). is to remove them from the track. Then place them inside of a mesh laundry bag, or send them out for dry cleaning.
You will quickly discover that the backing to the windshield curtains will very likely start to disintegrate due to UV exposure. And the backing will very likely disappear during an attempt at any sort of washing. If you do remove them for washing, it's probably a good opportunity to sew in a new opaque and UV resistant backing.