When you elect to participate in the trial you can set up as many workspaces as you would like and invite as many other people to participate in those as you would like. After the free trial expires, you will not be allowed to set up any new workspaces but can continue to use your existing workspaces. Plus you won't be able to invite new users.

The least expensive way for you to proceed is to purchase your license at the end of the trial period and ask others to download the free trial. Though they cannot set up new workspaces beyond the trial period if they choose not to purchase, you can continue to work with them in Groove and set up new workspaces.