Are you sure that you don't have any mod that removes child NPCs?
In general I tend to have a problem with the carriage with pathfinding when it reaches a specific bridge, most likely because I have a mod that modifies the area.
For that part sometimes by luck I manage to pass from there if I use moveto command to move the horse to a different spot and by accident it finds the correct path then.
For the last part at Rorikstead, this usually happens when you have mod that removes child NPCs, because there dialogues from child NPC when you pass from there.
If you have SexLab Sexual Fame installed, it has an option in the mod menu to remove child NPC, which is by default enabled.