I have an 8" bichir, a full sized knife and I used to have a full sized butteryfly, but everyone got along wonderfully. All three were very docile and calm fish and I never had any problems.
you guys are lucky... my senegal will eat ne and everything but my ropes, he was with 2 ghost knifes and a african knife for months and was fine , then they started dropping like flys, i left my camera on and caught the sengal kicking there buts so i had to separate them