I dont think they've spawned... I have a mixed group of wcmms and they've been together for months. No sign of even interest...
I think there would be some eggs left as they can have hundreds I do believe, so I highly doubt it...
This behavior may stop when you get a group larger than 3. I had similar behavioral problems, and all is well now because I upped the number to 5.
WCMMs are great! I am fond of them too. You know, I may do a wcmms tank myself...