From the sounds of it, this group were disruptive before doors closed, so did their behaviour escalate throughout the flight, or was it consistently bad right from the start?
If it did get worse, was the captain aware of potential problematic pax before departure, and were they kept informed regarding the groups' behaviour throughout the flight before the decision to divert? Or did the CC unsuccessfully try to deal with the situation themselves before bringing the problem to the skipper?
If the flight crew were aware on the ground still, did captain give them an ultimatum during the flight of behave or get arrested, or did it "come as a surprise" to the group when the flight was div'd?
Every situation is different, but I would have to consider telling the passengers to put up and shut up, or the plane would be diverted and they would be removed from the aircraft.
Over the pa if necessary. Apologising to the rest of the passengers for a small groups' behaviour whilst condemning the groups actions, and telling them (for all passengers to hear) that if they did not begin to follow all crew instructions and behave appropriately they would be arrested when the aircraft was on the ground.
Not criticising the crew, there isn't really enough information to say what happened. Just thinking out loud.