migrate data from Gdrive to OneDrive using an amdin tool - no dependancy on end users

Worth pointing out the SharePoint Migration Tool supports using a https://docs.microsoft.com/en-us/sharepoint/migrate-to-sharepoint-online/how-to-format-your-csv-file-for-data-content-migration, for bulk migrations specifying multiple source file share paths and destinations.

I'd mention also https://fasttrack.microsoft.com/, you'd qualify for the https://technet.microsoft.com/en-gb/library/mt651702.aspx at no additional cost. This would support a OneDrive for Business migration from a single G Suite environment (Google Drive only).

"FastTrack Specialists provide guidance on steps for data migration to Office 365. We provide guidance for you by using a combination of tools and documentation and by performing configuration tasks where applicable and feasible."

Might be worth looking into anyway. Also, this may be of interest - https://blogs.office.com/en-us/2018/02/06/make-the-switch-to-onedrive-for-improved-productivity-and-cost-savings/.