To answer mck16's question on relevance:
In my opinion, if MR did not have any groceries in the house for Dylan's weeklong visit, especially having had an extra day to prepare, it says to me he did not have much focus on Dylan's wellbeing or happiness. How happy would it make a kid to arrive for a visitation he did not want to do in the first place only to find he was isolated and there wasn't even food to eat in the house and he had no way to get to a place WITH food? Well, unless he immediately went to stay with other families that DID do things like feed their kids and kids' friends! Also, if MR stewed in anger over the flight delay and he has a history of bad actions when angry, I'd consider that VERY relevant, especially if its combined with signs that he didn't prepare for Dylan's weeklong visit. If there were few groceries the night Dylan arrived, did he bring back groceries with him from his errands in town on Monday?
On the second point, in my opinion, if MR never had a prior discussion with his brother at all about spending a day driving to his house to spend Thanksgiving with him, then I think it very unlikely that was ever in his mind at all. I would consider the possibility that he pulled that out of his hat after the fact when asked what plans they had simply to cover for the fact that there WERE no plans. That could 'possibly' be a cover also for why only a one way flight was purchased, if that is even true. I have wondered about that issue since MR's interview in the video store where he began to discuss flights but the video was shut off before he finished. If there was NO return flight, and there was NO communication with his brother about coming for Thanksgiving, I'd consider that VERY relevant to his mindset. It's not a given, but certainly 'leans' toward suspect.
There are always ways to explain why any of these factors are 'innocent', I'm well aware of that, and I agree to that. I just try to keep in mind the odds or likelihood of things. If it quacks like a duck, it 'usually' is a duck. But not always. Hence some suspects walk free until there is enough evidence to charge them.
All my opinion only.