You will need to make the Key field on the Fee Schedule table be a field which concatenates the three fields. One way to do that is to have a formula calculate that string and a form rule to change a data entry Key field to to the value of that calculated field.
Then in a relationship to the transaction details table, use a formula field to calculate that same string.
The string formula would be like
List("-",
[Fee schedule factor field 1],
[Fee schedule factor field 2],
[Fee schedule factor field 3])