Tricky Relationship for Conditional Value Lists

[Special Guests]

Hello,

I have two tables:

Guest

Scheduling

Guest

Full Name

Substitute Guest (Value list of all people in Guest)

Scheduling

Primary Guest (The Fulll Name from Guest)

Substitute Guest (This is the Substitute from Guest)

In Scheduling I want someone to select the Primary Guest and the field Substitute Guest will only populate people that have the Primary Guest name filled in in the Substitute field of the Guest Table

The problem is, it is tricky for me. How should I set this relationship up?

I had it one way, but it was inconsistant and changed from time to time on its own (it worked one day and not the other day).

I would love any help anyone would give me!

Thanks and God BLess!

David Garza