12 month old BT

[revers123]

I have a 12 month old Boston terrier male and 25 year old men pin females lately the Boston terrier has been biting the little man pens on the back of the neck leaving hard contusions and marking his territory around the house when hes completely potty trained. Hes a very friendly boy loves to play but does fight with this hands and his mouth what am I going to do I have now had to separate them all which is not good for any of them.

[revers123]

My male BT is biting the back of my 5 year olds MinPins I have 2 females
They taught him where to bite. Sooo what do I do. He is a big boy and has left a contusion on both. What do I do he is playing.