I had to get a six line out of my tank a few months back. Would constantly go after my Yasha goby and tiger goby. I will say I loved that fish and he went to my LFS
display tank. My suggestion is add the six line last Let all other fish establish territories then put six line in. I think that is your best bet for peace.
Remember they are hunting machines too and can deplete pod populations. So I also suggest well established tank before putting in.
By the way they are smart fish. Took me 3 weeks to catch him with multiple different traps.