The trick with keeping multiple tangs is to keep their body shapes adn colors different.
I had a blue hippo, yellow and tomini in my 125g and they were fine. I still have the same 3 tangs but have added a mustard like tang and upgraded to a 180g.
The most recent tang addition does look similar to the tomini but after a day of grief they all settled down. You may not be that lucky. Just some food for thought. Also, it is best to add all the tangs you will be adding at once. Cuts down on the aggression and the fish wont have territories to defend.