Manage iOS Developer Enterprise Programs for several companies I am a sole trader and I have developed an iPad app that I'm going to sell to several companies independently.
They are small companies (&lt;50 employees) that have nothing to do with IT and it would be a nightmare for them to register with the Developer Enterprise Program.

That's why I'm probably going to register for each of them. 

1- Can I register for several Enterprise Programs with my Apple ID, or does it have to be done by someone inside the companies (with a different ID each time that then adds me as as admin)?

2- In that case, am I going to be able to register on their behalf (if they provide me with their apple id + password? or if I appoint myself as the contact for Apple?)

3- Do I even need that program to deploy less than 100 apps to iPads?
You will need to use the Enterprise Program, unless you want to deploy everything on the iTunes store.

In terms of if you can register for several Enterprise Programs, a single organization can enroll in up to five iOS Developer Enterprise Programs.  However, each Enterprise distribution provisioning profile can only be associated with one App ID.

This Stackoverflow post should help.