I've had two Senegal Bichits for over 6 months now. They're both about 9 inches long.
I have had them with 2 three spot gouramis, 2 angels, 6 tiger barbs and 2 rainbows. They were living together in 55 gallon.
Recently I moved everything to a 75 gal and added 2 high-fin mollies (large about 4 inches long) and 2 swordtails (large at about 4 inches long but more slender)
In 3 hours, one of the swordtails is digesting in diver's (one of my bichirs) tummy and parts of the other two mollies (They were too big to swallow) is digesting in rocker's (My other bichir) tummy.
They have occasionally tried to catch my Rainbows but they are just way too fast for those near-blind bichirs.
The Mollies are slow clumsy creatures and so are swordtails.
My advice.
Do not put anything with bichirs smaller than 6 inches that is not fast enough.
My angels are slow but the Bichirs respect them cause even though they are **** in a physical confrontation they look big.
The gouramis are 6 inches so they get left alone. (NEVER been harassed)
Those little punk barbs are too quick for them too.
So yeah, either speed or 6+ inches.