[Fyron]

"The comps with "combat movement point" ability dont add they values as long as they are from the same comp family?"

Only the best is used.

"Do two comps from different families add those values (example: An engine combined with an afterburner comp). I was a long time out of SE4 universe and my knowledge is a bit rusty."

No. Only the best is used, irregardless of family numbers. You'll have to use different sized/ability components. Since they do not stack, there is no reason to use mounts. It will only increase design time. Just make sure that the components are clearly labeled as "only best is used, no stacking."

"fighters are totally destroyed in combat when hit, and not partially damaged in part of its components."

I'm not sure if this is what you meant, but... Fighters do take partial damage, and are not destroyed in a single hit. There is no damage to components for any type of units, just an overall hit point amount, and a shield point amount.