It's typical to have different ACME accounts on different servers (unless you have a rate limit exemption, then you usually need to use the same account everywhere).
You can update the email address of each account to the same address. It's just contact information, not a "username".
Renewed certificates are just new certificates with an updated expiry date.
Each place where you use a certificate must have some strategy for obtaining a new certificate at renewal time.
You could have one server which renews the certificate, and distributes it to the other servers at each renewal, using a Certbot
--deploy-hook or something similar.
As you can imagine, this complicates life. You now have extra problems to solve: how to implement this synchronization process, how to make sure it is resilient if a server is down, etc.
Having each server issue its own independent certificate is simple and it works, even if having many certificates isn't the neatest thing.