3.5.2 A charged time-out occurs when the ball is dead and: a. The request of either a player or the head coach (or the head coach's designee) is legally granted.
In our state, that has always meant one coach. It says or, not and. Does anyone, or any state, interpret that to mean more than one coach?
In our game Friday night the home team head coach said that he and his defensive coordinator would both call time-outs and the visiting coach said he and two of his assistants. They were both surprised, but did not argue, when we told them the rule book specifically says one.
To be honest, with less than 2 minutes left and the home team losing by eight, I know that it was the DC who called time-out behind me and I did not establish "visual contact" with the HC before granting the request as the Case Book tells me to. It did not seem like a good time to be picky.