I had my adult pair in my 30 gallon community with kuhli loaches, rummynose tetras and amano shrimp. I would never house rummies with kribs again because the rummies require more sedate tankmates. When they weren't spawning, they were fine community fish.
I can't say how it'll work for you in a 20, there's that much less space for the adults to get away from each other when one is caring for fry.
Both my male and female were highly aggressive during spawning. The male actually attacked the female on multiple occasions, ripping her fins, etc. The female was the primary caretaker for the fry and would actively chase the male away. He would chase the fry and eat whatever he could catch.
Both adults will consume the eggs/fry the first few times until they get the hang of the parenting thing. Then typically, one adult, either male or female, will become caregiver.
These fish spawn about once per month. If you do not have a method set up for getting rid of your excess fry, do it. My lfs will only take krib fry 5 months or older, as they can sex them then. That was too long for me and I didn't want to become a krib baby factory, so I gave them away.