>>Darby taught that God has two special groups of people (or two Brides) and a separate plan for each of them.<<
The church is the bride of Christ and Israel is the bride of the Father.
>>This meant Christ would have to return twice.<<
He does not return twice. We go to meet Him in the air in the rapture and then He returns to the earth at the end of the tribulation. Only one more returning.
I can see from scripture some basis for this interpretation. My faith and conviction is The Lord Jesus Christ centric for all mankind. Does Israel need faith in Christ to be saved?