Your ammonia is really .01? Wow, that's an accurate test kit you have. My kit reads 0, and then .25.
Maracyn 2 and MarOxy together should cure finrot very nicely. Bacterial infections are more common than fungal, and finrot is usually bacterial. But just in case, the little Mardel pamphlet says you can use the Maracyn 2 (antibiotic) and the MarOxy (fungal) meds together. I like these meds because they have an every day dosage, so it's easy to do a little water change before you add your dose for the day.
The Jungle Fungus Eliminator, for example, says to add a dose and then wait 4 days before a water change and adding another dose. I just tend to think that's too long. I do like that med, but I do a water change on the second day and add a little more med to compensate for what I took out.
Anyway, your Mardel meds will be fine.
Do you have a nitrate test kit? Check your source water -- I've heard of nitrates being in tap water (if tap is your source). So if nitrates are present in your tap water, they are being added to the tank with every water change. Overstocking causes high nitrates, but I don't think 2 fish in a 20 gallon tank is too much. How much are you feeding?
Live plants are a very easy way to remove excess nitrates. I have just a few low-light plants in my tanks, and my nitrates are about 0- 5
ppm. Some very easy plants are floating hornwort and java moss. You don't "plant" java moss either; it just sits on your gravel or driftwood.