Assume that we know that 'you' is Alex.
The shopkeeper opened the back door and looked out. ‘It’s
okOK,’ he said quickly. ‘You can get out of town along the river. Follow the back of the houses. Nobody goes there. Good luck!’
1. How should Alex leave
thetown? Yes, although it's not necessarily the case that he should go that way. It's just a suggestion by the shopkeeper.
a) By going along the river and following the back of the houses. I prefer this answer.
b) Along the river, by following the back of the houses. It's OK but it suggests that he can only go along the river by following the backs of the houses.
2. In order to get out of town along the river, what did the shopkeeper think Alex should do?
Follow the back of the houses.
That's fine though you've given a lot of information in the question, in order to obtain a very short answer.