Delivery Servers & Differnt Customers


I'm new here.

I'm working with Mailgun.

I have 2 domains, and 5 different accounts for each (meaning customers that I'm sending the emails via their mailbox. =,

Should I set up "Delivery Servers" for each customer or I'm setting it one time and it will catch all the others customers on the same domain?
As far as i know, mailgun does not allow from spoofing, so you won't be able to use a single delivery server which will use 2 different from addresses, so again, you end up using 2 different servers.
So I have to use the same API, but need to "setup" the server again with the specific user account mailbox and confirm it?