2 questions.

1. What size hex do I need to remove the front brake calipers?

2. To replace the rotors, is there any way around replacing the entire hub? Will rotors from a Ram truck work?

 

It would be helpful for you to note what year & model van you are working on.

Ram vans don't use hex bolts to attach the caliper to the carrier - the calipers float in the carrier and are retained by two spring clips held in with two 1/2" (or 13mm) hex bolts. The carrier assembly is attached to the spindle with hex bolts as well.

Rotor assembly is one piece containing bearings, races and seal and must be replaced as such unless you upgrade the entire spindle assembly.