Ok, I did it.
Finished division on insane, succesfully protected the Atlas and the Crane until it got evacuated (got destroyed later). Involved a little meta-gaming, but it worked.
Almost died at the end to a stupid manticore :/
Send alpha 4 and delta wing (myrmidons) to protect the Reuil, send alpha 2 and 3 to engage the enemy, let beta (ares) defend the crane, later the atlas. Tell all fighters to ignore the Ravana (maybe not necessary, but did it all the time anyway to prevent the wingmen from doing stupid things)
That takes care of the Reuil without problems (alpha 2 and 3 are invulnerable, they will charge first, get attacked by the Maras but don't die, while delta will kill the now defenseless bombers)
After libra jumps in, shoot down 1 or 2 fighters, then go to the other side of the Crane and intercept the first wave of cancer, let one live and make him attack you, then tell everyone else to ignore it. Keep in skirmish, while beta defends the Crane and later the Atlas against libra.
Sometimes a Mara breaks off from the fight at the Reuil, you have to survive and kill it somehow.
Now, on to the next missions!
The really ugly thing about cancer wing is, that it spawns on the opposite side of the Crane, so they will be ignored by your wingmates (those still fight with libra) and destroy the Crane almost unbothered, and even if you attack them 2 or 3 will fly past you.