Unable to deploy Cobras and Maraders in Peace talks?

[ministryf79]

I am wondering how to make sure when I unlock units I can use them in the solo mode. I seem to be having problems understanding how the tech tree/unlock units works. I have unlock the cobras and marader anto tank nits but I am not able to deploy them on mission 5 peace talks?
Any info would be great thanks. I am pretty sure its the way I am unlocking units in the armory.

[КРАБ]

wat

[PLNTRXS]

Marader no, Marder yes.
There are only 4 Cobras in this campaign, if you lost them in previous mission you must play again and keep some alive.
Same for Marder.
But these 2 units are not 100% necessary to win this mission.