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I see no reason why the two species sited can't be housed together in a 28-gallon tank, just so long as your setup includes numerous shells and caves for hiding places.
You will want some type of visual barrier between the groups though, a couple of large rocks will suffice, along with some plants. Some Cryptocorne affins or wendtii are a good choice for the substrate, and some Anubias nana for the rocks.
As long as you have one pair of the occelatus it should work out fine.