I don't really know about diseases and stuff, but I have personally used plain, active culture yogurt to firm up runny poo. It will help nourish them and add friendly flora to their digestive system. If they like the yogurt plain, great... if not, mix about 1 tsp in with their starter to make a moist mash. Another thing that would not hurt and just might help is putting apple cider vinegar in their drinking water. I'm not sure how much - I just use a tiny splash for a chick waterer - but you can search the forums if you would like more information.
Good luck! I hope they are OK!