It sounds to me like you should have 2 relationships to Work Orders. One where Projects is the Parent and another where Work Projects is the Parent. Work Projects would also be a child to Projects. Then, in the Work Orders, you would want to setup Related Work Projects as a Conditional Drop Down that uses Related Project to limit the selection of Work Projects to those of the selected Project. This way, you would always have the user select the Project, but the Work Project would be optional and your Project Name field would be brought down as a Lookup from the relationship with the Projects table.
