Suspected player using 3 accounts in 1 game.

I had a player give me an outlandish reason why he had 3 accounts in one game. I know it might be true a family of 3 could be playing together, but he said the main player was coaching them. He then said they were pro gamers 2 brothers, being 'coached' by their dad. Would this coaching not indicated 1 person was playing 3 accounts in 1 single game???? Both accounts were made at the same time, after the main account was made. This was indicated by the numbers being identical. Is it not against the TOS to used 3 accounts from the SAME IP(im assuming) in 1 game?