First let me say my puppy had an appointment tomorrow morning with our vet (earliest we could get in without a $400 emergency vet visit)

I have 3 puppies same age from same litter..

Thursday one got sick vomiting and blood poop, almost nothing but blood, acting lethargic, wouldn't eat, drink etc. Sat he started drinking, Sunday he started eating now he is back to his playful self, eating, drinking but still loosing weight.

Another got sick Monday pooping straight blood and was gone within hours.

The 3rd is so far 100% fine with no changes at all

Any advice on what could be going on?

** also I did not make the appointment until Tuesday since puppy #1 was getting better and puppy #2 didnt get sick until late late monday night/ early Tuesday morning, I DID call when he got sick and was advised to keep an eye on him over the weekend.