I did have two six inchers years ago and they hid together in a tree stump for much of the day.They came out at night to look for food.Mine is pretty peaceful as it spends it's time moving back and forth across the tank,it hardly ever squabbles with my smaller dats.
Hard to say.I don't remember what happened but I didn't have that duo for very long.With enough space a group of them just might work.
There's plenty of open space in the 210, but there aren't any hiding spots for three 15" knives. I can only keep three if they all school like the quote mentioned... Otherwise they'll kill each other over a spot that can only fit half a knife.
I don't provide anywhere for my boy to hide but I do keep things dim as I rarely use the tank lights.Ive gotten away from driftwood and large stones for the time being and my fish have more or less grown up not depending on having hiding places.If anything,I'll use a few fist sized rocks so as the fish grow they become accustomed to being out in the open.
