During the funeral scene, Dave and Harper (Steve Zahn and Kathryn Hahn) sit next to each other, and in between shots Dave's hand jumps from being behind Harper to holding her shoulder.
A body cannot be cremated into "flush-able" ash from a fire. It does not get hot enough. Even in a proper crematory, the bones have to be ground up to be unrecognizable.
In the scene around the fire in the evening, the family faces the fire and holds up books to read. This would block the light from the fire, and the pages would be in darkness, meaning they'd be unable to read.
When the family visit Leslie's grave, there is already a tombstone in situ. In reality, a tombstone is usually not carved and erected until months after a burial.
When the state trooper pulls the bus over, he says that the left back tail-light is out, however it is the middle of the day.
When the family parks the bus at the trailer park and Bodevan is talking to the girls, you can hear George Mackay slip back into his British accent.
While rock climbing, Zaja states a fall could result in a "splenic flexure of the large intestine", which isn't an injury. it's just a portion of the large intestine (the bend from the transverse to descending colon that occurs close to the spleen).
The college acceptance letters that Bo receives in July 2015 all invite him to join the Class of 2016. Assuming he applied to start college in the Fall of 2015, there are two obvious errors with these letters. First, Ivy League-type colleges usually accept students in late-March or early-April, so receiving letters in July is unlikely. Second, even if the timing wasn't a problem, the Class identified in the letters is wrong; Bo would be in the Class of 2019 if he started in the Fall of 2015.
When Kielyr is about to shoot the sheep with her bow and arrow, she has the arrow on the inside of the bow, so that the arrow is between her and the bow. It should be on the outside of the bow, so that the bow is between her and the arrow.
When father and son first take the bus into town, views of the sky are shown, in one of these shots a reflection of the camera lens can be seen in the glass window.
When Ben and the kids are pulled over by the policeman, the policeman sees the kids and asks why they are not in school. Later, it is revealed mother died in mid-July, meaning the movie is set around the same time, maybe in early August at the latest. The movie is also set in the United States and most schools in the U.S. don't start until mid-August at the earliest. The time frame of the road trip would have placed the kids in summer vacation to any outsider unknown to their real situation, including the cop.
Ben's children quietly escape from Jack's house, hide in the bus unbeknownst to Ben. He leaves the house when it's daylight, and then the viewers see him making a stop when it's already dark, and that' when the kids come out of hiding, surprising him. That means at least several hours have passed since Ben departed from Jack's house, and he was driving the whole time, not making any attempt to hide.
Being a very powerful person, Jack could've called the police right away upon discovering that his grand kids were all gone, in a matter of minutes. The police would've then stopped the bus and searched it, likely finding the kids hiding in it.
If Jack decided not to do it, it is unclear what his motives were, what made him change his mind.