- The Resources collection returns the content of what you see in the Resources panel/field of the project. The Sales VP or accountant you mentioned are probably resources of the project in that sense. What do you expect 'the members of the project' to be?
- The JobTitle field (like other fields in the inner Select) is a field of User (their Job title as it appears in the People module). If you have a null value there it probably means a Job Title was not set for those users (or for some reason your API user has no permission to see it). Where does the 'role' information you expected appear?
Hope this helps,