Currently handover, with indirect homicide my second thought. MOO. L&J were not known to wander, and the dogs only picked up their scent to the end of the driveway. I don't believe either parent committed homicide; I think there would have been evidence of the crime, if not the hiding/disposing of the bodies. I could see a case where they negligently failed to secure drugs/meds, but I think bodies would have been found by now (or cadaver dogs would have been deployed). Stranger abductions are relatively rare, especially in pairs, and in cases like the Groenes, the rest of the family was murdered before Shasta and Dylan were taken.
So, my current theory (which has a massive hole at the end) is that DM is not involved in the handover plan. MBM wanted out, and arranged for people known to her, most likely in her band, to pick them up early on May 2. She told J&L they were going on a little "vacation" and she'd be joining them later. She walked them out to the road, where their scent trail ends, and they're picked up by car. She went back inside, and DM is still asleep. She brings Meadow into bed and pretends to be "drifting in and out of sleep" and concocts her story about what she heard and whom she heard. When DM wakes up, she panics and tells him J&L are gone, puts a story in his head about what and whom he heard, whether both J&L came into the room and how many times, etc.; the stories differ slightly but both stress how easy the kids would be to kidnap, how they'd go with anyone, and how they never close the silent sliding door. Two days later, MBM takes Meadow and heads off to wherever J&L are.
The massive hole in this story is the RCMP, of course. I don't exactly how they coordinate policing wit First Nations bands, but if they knew the kids were safe with the band, I'm sure they'd make a statement that the case is closed and the children are safe.
All MOO.