365 license

I have users (20) in our corporate with laptops with Office Home & Business 2010 / 2013 and 2016 licenses.

We are in a process of migrating from Office 2016 to Office 365 in our RDS environment.

My question is related to access/license for users with existing working licenses. 

Is it possible to have the 20 users use their Office licenses to work on the Terminal Server and access Office 365 ( I imagine it would have some limitations) or I need to purchase more licenses for these particular group (20 users)?

Please, advise.

Thanks,