Yes, in my opinion too small,sorry. You would need at least a 10gallon because the catfish are active! I have a 10 gallon with 4 Julli Catfish,same size as the Pygmy and wow, they are all over! The bio load will get to be too much as well. And, you need places for them to hide from each other (which I'm sure you knew already). Not sure how to make that work in a 5 gallon, I only had critter keepers, 1.5 or my now 10's. There are others here that know better then me! This is my first time mixing them! They are so cute though! :) Good luck!
Betta's: "Mint" & "Flare-Boy"
Other:6 misc catfish,Tetras,Glofish,Mollies
*RIP* To all my past little ones