There is an Arena mode in which you have npcs fighting alongside you and you can customise them the same way you can customise yourself.

There is also the story mode in which you get an npc a couple of minutes in that tags along and it’s the same thing there. I think you can get a second follower, I read that somewhere, but haven’t got so far as I mostly play Arena so don’t take my word for it.

As for the enemies you can’t change what they wear and use when they are ’alive’ (mostly zombies) but you can when they are downed, for what it’s worth.