I found spots of blood in several places at home today, both cats are ffemale and fixed, what would cause bleeding.

The simplest explanation would be that one of them got cut. There are a million different ways that could have happened. Your best bet is to check them both thoroughly to see if you can see any blood on them anywhere. If not, and they both seem fine, I wouldn't worry about it unless you continue to find blood. Sometimes they cut their paws on things, and sometimes they get each other with their claws when they're playing. Also sometimes their gums. I would check their paws and gums first, and then feel around to see if there is a scab beneath their fur.