I think OP is asking about how to use different skeletons without having to make new animBPs for each one.
I haven’t gotten too into this myself but I think probably the thing you need to do is actually make sure you are using the same skeleton for every character you animate. But, let’s say you have a male and female version of the character that share the same skeleton that need to use different animations, you would do all your logic in a parent animBP for, say, the male and then create a child animBP of this for your female and use animation blueprint overrides to change the animations you want to use the female set.
In short, as far as I know, you can only use one skeleton per animBP so make all your characters that need to share an animBP with the same skeleton.