Crisis suits do not (normally) have 2+ saves. Barring soecial equipment, they have 3+ saves like PA
Also note that crisis suits are 2 wound models, and you have to assign all of a model's wounds before moving on, so in the case of 4 wounds against 2 suits and a drone, there is no 'wrap around'
So in this case, you could assign 1 wound to the drone (which gets an invul save) and 2 wounds to one crisis suit (which dies) and 1 to the other.
The drone does not get to make multiple saves unless a whole lot of wounds are scored, and considering these are AP3 weapons, it wouldn't matter anyhow since that many wounds would wipe out the suits and thus kill the drone.
Nor does the drone grant an invul save to anyone. If you want invul saves for your suits buy a shield generator for each one.
So here's how it should have gone.
you score 4 AP3 wounds.
He assigns them to one suit (the one WITHOUT the drone controller if he's smart), the drone, and the last wound to his last suit.
The drone (and only the drone) rolls his invul save. If he makes it, the drone remains, otherwise he is removed with the first suit.
If, for some reason, he chose to assign the two wounds to the suit with the drone controller, then the drone is removed automatically...though since casualties are resolved simultaneously, it would still get to at least soak up one of the wounds.
If the drone IS removed, then the remaining (wounded) suit must start making Last Man Standing rolls. If the remainign suit has the drone controller, and the drone passed its invul save, then the (now reduced) unit makes a morale check for 25% shooting casualties and, assuming they pass, fights on as normal, otherwise they fall back.
Moral of the story: Buy more drones, because just one is kinda useless. If you want invul saves, buy shield generators and, for the love of god, always buy a bonding knife for your battlesuit units. They're small, expensive units and need to be on the field as long as possible.