I am new to finch keeping. In our aviary we have: 2 male cordon blue , M/F Gouldian, M/F Green singers, and 2 societies. Everyone seemed to be doing fine until yesterday. The two male cordon blues have seemed to be good friends. They have started singing/dancing and building a nest together. Occasionally they get in a squabble, chase each other a little, pull a few feathers. That I can handle. Today I saw one of the blue finches harass one of the society finches. Sweet innocent little societies

I was sold these two blues as a pair and was told all of these finches could get a long. I was concerned about the green male singer being a bully, and was told the blues were more passive. Not the case at all for my birds!
Is this breeding behavior? Should I take the nests away? Do I need to return the two blues? I don't have room for more birds so buying two female blues isn't an option. Having a second cage permanently isn't an option either.