I have a 55 gallon tank with 3 rope fish, a ornate bichir, a dalhousie bichir and a senegal bichir. They have all got along great. The bichirs are from 2" to 5" and the ropes are 9" to 14".
The only problem that i ran into was the senegal got aggressive with ever one in the tank, even the 9" pleco so i traded him in for another delhousie.
But that could happen to any breed, some are calmer than others and then there's the odd nut lol