In the overhead shot when Tom is walking toward Sandra with the bag containing the money, he hands it to her and she puts it over her right shoulder, and then they start walking. However in the next immediate cut which is a close up of them standing and talking, the action of Tom handing her the bag and Sandra putting it over her right shoulder is repeated.
The seat belt sign is on while the plane is taxiing so the flight attendants would have asked the character to return to their seat immediately.
While sometimes toilet doors are locked while a plane is taxiing, this is not a universal policy and is usually only done depending on the individual flight attendant's preference, so it is not unreasonable for the character to be able to open one.
When Madeline and Sandra are in the cab on the way to see Max, Sandra asks Madeline where are they going. However they are in a Yellow cab therefore Madeline would have told the cab driver the destination and thus Sandra would have known where they are going.
Max caresses his mum's hair and head without having washed his hands after peeing in the bottle and the mum does not seem to mind.