you can't keep any bichirs in there, tank is too small.
I would say 45-50g long is the bare minimum tank size even for a single sen.
One of my sen is pushing 35 cm, and I've also heard that a sen can grow up around to 50cm in the wild, where as in the home tank, expect around 30 cm growth for most sens.
I'd say the minimum length of the tank you should have is three times the maximum length of the species,
where as the width would be at least the maximum length of the species.
Bigger is always better.