CB Bangaii Cardinal Behavior

[OracleOCA]

These are my first fish in my reef tank since they are less aggressive then ocellaris clowns; I plan on getting two CB clowns in a month or two and that will be all of the fish I get for my 40g.

I purchased three captive-bred Bangaii cardinals from ORA via Petco two days ago. I picked them up as soon as they were dropped off at the store so they only needed to be acclimated into my tank ( I acclimated them for nearly six hours just to be safe using the drip method). They appear to be eating frozen mysis although I really only saw the two of the three eat. It is hard to tell them apart and they are about the size of a nickel. According to ORA, they are approximately six months old. They seem to stay in the botom corner during the day but are all over the place when the lights go off. There are two that are starting to hang out together in a cave and the other and by himself. There is no aggression of any sort between them so I am assuming there is one male and two females??? They also make this thumping/clicking sound between them. What is going on with them? I cannot seem to find any detailed information on these lovely cardinals. If there is a book, please inform me so I can read more about them.

Thank you

Janie