Please don't add any catfish to your tank, they are a serious danger to your Axies.
There are some real horror stories with mixing species, so check out the other threads on here.
Maybe you could add some glass shrimp or cherry shrimp, I hear they are OK and are good at cleaning ? Plus they make a tasty snack for your axolotls too.
With your Axies lack of activity - most are bone lazy and will lay around doing nothing for long periods of time, mine sleep nearly all day until dinner time then they get active....
Not sure what to do with the algae, I've never had any but I'm sure if you post all the information about your water parameters, temperature, tank size etc. I'm sure the experts here will be able to give you some great advice.
Good luck, don't forget to post that info and some photos of your tank might help too :happy: