Three bluetooth arduinos at the same time

It depends on what you are trying to do. The Arduino BT is capable of a single serial connection (SPP in bluetooth terminology).

If you want all three BTs to talk to a single computer, that's OK. If you want each BT to talk to the other two, that's a problem, as you'll have to talk to only one at a time.

The bluetooth stack in the module on the BT is highly simplified so that the microcontroller doesn't have to implement the entire bluetooth stack. One of these simplifications is a single SPP connection (instead of the 60-something that the spec allows).

I don't know if bluetooth will operate in a mesh-type network, or if it requres something to be a master.

-j