It's best to hang the doors FIRST before you mortise out the locks or flush bolts. If you getting the doors pre-hung, make they mfgr doesn't do any pre-drilling. Get it on the order form like this so there's NO mistake. The reason being, if the locks are installed BEFORE you hang them, you may have a problem lining up the doors. That's why Ed suggestion of leaving 1" for the jam width is important. If you have to 'tilt' one or both of the doors, the lockset might not line up properly. So, hang the doors, THEN mortise them if that's what you end up doing. The equipment to do this is best used by a professional. (You may not want to go this route but if that's all a pro has to do for you, you've still saved yourself a lot of $$$ by doing the bulk of the installation.) Work with a door 'hanger' on this and you can schedule this part of the job w/him.
We have a T-astrigal installed on the active door to 'hide' any gap. Again, my best to ya and hope this helps.