Lucifer had been waiting. He had been biding his time, patient and confident the twins would fuck up eventually and he could snatch them away.
When they stepped onto the sidewalk and outside of the warded area of their home, one of his minions immediately let him know. It was a Sunday morning and the saints were at church. Oversight was minimal.
Lucifer set to work. He sent the Doppelganger in and then he popped into place, right around the corner from the twins, waiting until he knew Michael was properly looking the other way.