What you do is: First up build your defences on your base.
Build about 5-7 scorpian tanks and 3-4 hornets, upgrade them if you can.
Focus on the flood area in front of you and send you tanks.
With your tanks, focus on the defences (one by one) and then call your Hornets to kill the infantry. (Make sure you destroy the central base or they will regenuate)
After that that one should be clear. You should get a Tank once you rescue them.
The second one is harder. Rebuild you original force and send you tanks like last time. But once the fog of war clears use the cyrobomb to freeze the defences and focus on them 1 by 1. use the hornets to mop up infantry.
The last one use your remaining force and take out the defences.
You should now be in control of the group you needed to save. ( because the pelican retreats )
Now with you complete army micro control them back to you base and make sure they stay as a group, and with that you should complete the level.
This should work as it did with me