You can create a new group and further restrict the access using record rules for this group. This helps in managing the access better without overrides. 

If you inherit the access of project/admin to this new group, it'll have all the access of project admin and will not serve the purpose of restrictions. 

Rather you can duplicate the project admin group, rename it and then  remove the access which is not required for the users of that particular group. Then add the record rules to this new group to further restrict access to the users to access the records which is related to them.