Help bloody wet spot on floor

Last week I found three bloody wet spots on the floor. On in the hallway two in the livinging room. I have two cats one 8 months one 7. Both are fixed. I also have a 4 year old westie. The spots were dryed with no matter in them. They didn't have any smell. I thought maybe one of the cats got sick. Diarrea, vomit and the dog cleaned up the mess.I had been giving dry as well as on shared can of wet to the cats daily. The wet comes in a variety pack and the last wet was a seafood of some sort. I stopped all wet food. I checked the litter box but as I have the litter robot all the nastys were entirely covered and everything looked normal. I did notice that one of the animals had gas. Not sure who, as they are always rsting near me when we watch tv. Well, a week later, this morning I find another spot in the hall way. It is still wet. Not like bloody, just like watered down bloody. It has no smell. All three animals are acting fine. Playing, eating, drinking ect. I looked at all their bottoms. The female has dark small crusty spots around her rectum. She does not smell and has nothing in her fur. The male cat has a very clean bottom. I would like to take the sick animal to the vet but how to tell which it is? I will try today to follow the cats around to the litter box. Any other ideas. Anyone ever see spots on the floor? The kittens were worm before they were sent to me. The female last week coughed like she had a fur ball for only a few seconds and then went back to playing again. I have noticed her drinking from her drinkwell. It could be normal amount though, as I am now looking at everyone under a microscope. Here are the ingredients of the kitten food I am using.
Crude protein....36%
crude fat..........22%
crude fidbe........2.5%
The list goes on. The first ingredient is chicken, chicken meal, corn meal then poulty fat ect.
This is maxximum nutrition brand what the breeder was feeding.

Oh my - it's always hard to isolate the sick cat in a multi cat household! It sounds like your convinced that it is a digestive problem. How big are the spots and are they splattered or in chunks like vomit?

When I have these types of issues, I simply isolate the cats from each other for a while. Since I have so many, I'll put 2 or 3 in a room at a time to see if I can narrow it down, then isolate them further until I find the right cat. Maybe rule out your dog first then separate the kittens for a few days. It will break your heart and you'll have to remind yourself its all for their health.

Could be colitis. One of the cats might have an irritated digestive tract and that can manifest as blood. You need to unplug the litter pan scooper and see if you can see who has the bad poo. The one with colitis will have some mucus with it that could contain blood.

My oldest cat had that when I first brought her home. She had a week on an anti-inflammatory in Pet tinic drops and it cleared up. She never acted sick.

The gassy critter is also an indication that this is what it could be.