Why would users be editing the lookup tables? If lookup table record is edited, that edit will reflect in EVERY tblRequests record the lookup record is associated with.
Normally a form does data entry/edit for only one table.
If you want to allow users to edit the lookup tables, that should be done on a separate form. If you want to allow users to add new lookup records during data entry to tblRequests, explore use of combobox NotInList event.