Had just this situation on Friday just gone.
3 Aircraft, Class 'G' airspace, all on a FIS and VFR at similar levels and aiming for the same square mile of airspace. All were wearing individual squawks so I knew who they were, but couldn't really give radar derived information.
So, under duty of care - just tell each one where the other two are and where they're going - let them sort it out.
Worked a treat
CM