User groups vs Project Groups

I have different users groups that need the same access levels to a range of projects.
This is different to the current project grouping.

For example contractor_group_a, may need access to 5 projects as a developer and these are spread across the current project groups. A second group ‘simulation interns’ may need access to another group of projects, some of these overlap with the first group.

I’m not sure how to manage my different user groups effectively within gitlab.