Is there only one bird that he is fighting with or all six new birds?
He has to settle the territorial issue, and obviously he thinks he owns the whole place. They should settle down soon, if they don't, you may not have enough room or perches for them all.
If it is just one bird he is picking on, then you need to keep an eye out on this underdog, it may be a gender issue also, if you have introduced hens to an already exisiting bossy male pigeon, who thinks he owns the place, watch out.