Oh My,
do they have runny pooh? whats there Temps? did they eat any pork, chicken or processed meat, like bologna, turkey, hotdogs? Have they been in a lake or swimming pool?
Near bug spray like the kind used to spray condo's, new paint or have you changed dog foods lately to anyhting with NATURAL FLAVORINGS in it?
All these things can cause stomach probs and blood to appear. Can you confine them to carriers to see who is ill? Please call your Vet asap. My oldest did this 2 times. Once after swimming in delta "Duck Pooh in Delta water" and once after eating chicken lunch meat. 3 days of vomiting and bloody fluide. It was very scary but it passed on 3rd day.
I hope all gets better