Associating SubForm Records with a Second Parent Form

Associating SubForm Records with a Second Parent Form

I'm a bit lost on how to associate a subform with a second parent form. Im my use case I have three forms: 

Parent Form 1: New_Potential_Tract
Parent Form 2: New_Working_Tract
SubForm: Ownership_Details

New_Potential_Tract has a bidirectional relationship with Ownership_Details via a field called "Tract_ID_Code".

New_Working_Tract has a lookup field "Potential Tract" allowing the user to select the Potential Tract to convert to a Working Tract. A Deluge Script then pulls field values from New_Potential_Tract and populates the values in New_Working_Tract.

if(input.Tract_Name != null)
{
data = New_Potential_Tract[ID = input.Tract_Name];
input.Team_Drive = data.Team_Drive;
input.Tract_ID_Code = data.Tract_ID_Code;
}

However, I cannot figure out how to associate the Ownership_Details records with the New_Working_Tract. I tried creating a second lookup field in the subform, but didn't have any success. I tried modifying the Deluge script to fetch the records based on the Tract_ID_Code (the same field used by New_Potential_Tract), but again didn't have any success.

if(input.Tract_Name != null)
{
data = New_Potential_Tract[ID = input.Tract_Name];
input.Team_Drive = data.Team_Drive;
input.Tract_ID_Code = data.Tract_ID_Code;
SubForm = Ownership_Details[Tract_ID_Code == data.ID];
Ownership_Details = SubForm;
}