I can't see why Dylan would set out for his friend's house, knowing his dad planned to drive him there around noon, especially without checking too see if R was still there waiting. If his phone had lost its charge AND he had no charger, despite his mom saying he did, I believe he would have just waited for his dad. Hitching is what you do when you can't get a ride.
So. IF he overslept, and IF his phone did not work, why not just sit there and watch some more TV? Dad would be home, Dylan could call or text R from his phone and they would be on their way. There has been no indication that Dylan would be inclined to go outside and play alone while waiting, nor can I see that happening. Play what?
We either have to believe he decided, for some reason, to blow off his father, not even leaving a note, and try his luck at hitching a ride; that someone came inside and convinced him to go away with them, for foul purposes, still no note; or that he was physically unable to contact R that morning due to something having occurred on Sunday night or Saturday morning.
Based on the odds, number three seems most likely to me. I would not lean this way if Dylan had a different background with regards to his parents, their hostilities, etc. but he didn't. He had two parents who had been battling for years, the visit was court ordered, etc. not exactly the setting for a blissful reunion.
I am not determined to point at his father, it just becomes more of a possibility to me when I look at the other options. Child abductions are far rarer than incidents between fathers and teenage sons.
If Dylan does not magically reappear sometime in the next 16 or so hours, I doubt very much he is being held by a family member at the request of a parent. No one who cares for Dylan is going to force him to stay away and miss Christmas Day.