Johns Hopkins Aramco

My wife has accepted an offer as doctor at Johns Hopkins Aramco but we are very confused moving there from USA. The process is very slow and we fear that we will miss the school start date in August (DEM and DHS). Does school keep the student's seat if they are late due to visa issues?

Also how long does it take to get the family visa after arriving in Dhahran? We want to arrive as family but not sure how to persuade the relocation advisor.