What version of a plan would I need for this environment?

What version of a plan would I need for this environment?

At a client site there is one computer that controls the building's HVAC system, that is located in the superintendant's office.

The following need to access this computer remotely - without any interaction required from anyone in front of that computer:

The super from either of his tablets (iPad / Windows 10).
The building's office manager from her Windows 7 desktop.
The software vendor's rep from outside the site.
Me, for quarterly computer maintenance.

What version of ZOHO Assist would I be looking at purchasing?

Thanks!