PG's latest point is sometimes true, sometimes not. It really depends on the school and the contract you sign. In my current school, if you apply as a couple, you get a couple's contract, same as a married couple. If you break up, the same rules as if a married couple get divorced.
Two schools ago, the options were married (two inter-related contracts with family bennies assigned to one of the two people) or single (two separate contracts with each getting all bennies). No room at that school for a couple's contract. A couple could have a shared apartment, but if they broke up, they would have been entitled to separate accommodation.
So you need to explore how each school handles it.
Middle east: Unmarried teaching couples
Discussion
While @Sid and I dont entirely disagree, finding out how an IS handles there contract can be very difficult to do, and to get to that point an IS has to be at the point where they are ready to hire you. The idea that your going to spend X amount of the time you have for an interview or recruiting explaining why an IS should consider you a teaching couple doesnt really happen.