Do I Need to upgrade or is this okay?

I currently have a 20 gallon fish tank. In the tank I originally had two dwarf cichlids, a dwarf honey gourami, five pristella tetras, a marble loach, and a baby bistlenose pleco.

My mom had a 20 gallon tank as well but she could no longer look after the fish she had. So she brought them over and asked me to look after them. I told her that there were too many but she pleaded and I can't so no to my mom (easily).

So now, along with my fish there is a kissing molly, two glowlight tetras, two zebra danios and a cory catfish.

My first question, is a 20 gallon tank too small for the amount of fish? Second, if it is too small, how soon should I get a bigger tank. Currently I am looking for a second hand tank. New tanks can cost $500 - $700 and I can't afford that. So will they be okay until I find a bigger tank?

And please no judging. I never planned on having this many fish and I am doing whatever I can within my power to fix this problem, if it is a problem.