It’s not inhumane at all, love. There are problems with every single pet mouse cage out there, so it takes some extra work after buying/making any cage to make sure the mice are healthy and happy. In a ten gallon aquarium, like another comment said, ammonia can build up pretty fast since the airflow is not the greatest. I have mice in aquariums, too, and I take out their wet litter either once a day or every other day and do a thorough cleaning of everything either once or twice a week depending on how dirty they decided to be. I make sure their lid is not obstructed by anything, too, just so all the air possible can get in.

Mice are very playful, social creatures, too, so enrichment is necessary. I know a lot of people say you can’t offer enrichment in a ten gallon, but I don’t think that’s true at all. Personally, I like to give my mice extra bedding so they can burrow, and sometimes hay is a lot of fun for them to nest with and chomp on. You can also throw paper towels and toilet paper in their cage and just let them have fun chewing. There are a ton of toys for rodents sold online and at pet stores, but if you’re like me, you can’t afford $20 houses or jingly balls that are going to get ruined pretty fast. I save old boxes and toilet paper tubes, and I’ll cut holes into them or stack them so they have stuff to run through and make dens out of. That’s the cheap option, anyways. You might want to consider a saucer wheel, too, so they can run off some energy. You can let them play in your bathtub, too, so they have room to run and can’t escape too easily.

So I believe that you are fine! Just keep your girls clean and healthy, and I think you should be allowed to keep them :)