I've got 2 sen's in a 55 with a jack dempsey, pictus cat, african brown knife, leopard ctenopoma, small convict, peacock eel & shoal (8) of tiger barbs.
I don't have any issues. The dominant figures in the tank so far are the jack dempsey & pictus, they each have their own side of the tank. The leopard & the convict squabble sometimes, they mostly ignore the pictus but sometimes are at odds with the jack dempsey. The bichirs prety much keep to themselves. Occasionally they'll nip at eachother, seems to be minor territorial aggression. The tiger barbs are oblivious to everything they just chase eachother around. Sometimes the knife gets chased by the leopard & the eel is completely ignored by everything.
Basically...strange mixtures of fish that would sound like a nest full problems are entirely possible. It took a bit of trial & error to get things situated, but right now everything seems quite happy. At the moment I'm trying to upgrade to a 90gal where they'll stay for the next year or two, at which point I want something like a 125-180 to house them all
