#1: I already have an unexpired FAA Flight Instructor certificate single engine but not instrument (for example). Do I have to take the new MCI test to add Instrument Instructor or Multi Engine if I teach those in the military? No, you don't.:

The FAA has decided that where a current or former U.S. military instructor pilot or U.S. military pilot examiner already holds an unexpired FAA flight instructor certificate, they do not have to undergo another knowledge test as required by Sec. 61.73(g)(3)(i) because they already possess a valid flight instructor certificate. So just follow our guide for the application paperwork, and take it to your nearest FSDO to add your additional flight instructor ratings.

Here are the applicable words from the new 14 CFR 61.73:

(i) A knowledge test report that shows the person passed a knowledge test on the aeronautical knowledge areas listed under ยง61.185(a) appropriate to the flight instructor rating sought and the knowledge test was passed within the preceding 24 calendar months prior to the month of application. If the U.S. military instructor pilot or pilot examiner already holds a flight instructor certificate, holding of a flight instructor certificate suffices for the knowledge test report.