Same NFS share on different clients with different local users

Solution 1:

Ownership of files can't be split like that. The files on the share can only have one owner (UID) and one group (GID). The names of those groups could be different on different clients (e.g. UID 1000 is "smith" on one client and "jones" on another), but the actual UID/GID values are stored on the NFS server file system and will be the same for all clients.

If you want to have common access across multiple clients with local users, then you'll have to have common definitions of groups on all clients (e.g. the "dummy" group has GID=1001 on all clients). The members of the group could be defined locally.