When was the last time the timing belt was done?
And are you changing the other belts just cause or are they showing signs of age/wear or has something broken?
All the belts are usually done at the same time, the 3 that you want and the timing belt. Unless the timing belt has been done recently (while you have owned the car) then it should be done as well, even if the previous owner says it was done at xxxxx miles or on whatever date.
The timing belt job also includes the water pump, timing belt tensioner pulley, and valve cover gasket at a minimum.