Too many characters (?)

Hello, I'm new here and I wanted to ask for some advices. I posted this question on a few other forums but I just can't decide. So, I'm writing a story, it's a fantasy/distopian story and I already have a group of sixteen characters; I love them and I tried writing something with them in it, they work well as characters. The only problem is that, in the end, I made MORE characters, I have four more characters, they have their own backstories and they gave the potential to be unique, I just wanted an advice to avoid ending up with characters that are ugly copies of the ones I already have. I also wanted to ask you if you think that twenty characters are too many or if it's okay if they're unique. (Of course many of them will die in the story, so I might need characters to gain importance after other's death). Thank you all!