The trick is as follows:

1) Loyalty for all. I don't know if this is 100% mandatory, but it doesn't hurt.

2)Research everyone's special tech contributions. Same as point 1 - I don't know if it's mandatory, but it doesn't hurt.

3) To get Legion's loyalty in time, talk to him directly after you get him and do his loyalty quest immediately. Your crew won't be abducted until after the quest so long as it's the absolute first thing you do.

4) After your crew is taken, go find them immediately. You can save most of them if you're quick.

5) Choose Tali to be the tech specialist.

6) Choose Garrus to lead squad 2.

7) Choose anyone loyal to escort your crew back to the ship.

8) Choose Jack as the biotic specialist that creates the shield around your party.

9) Once again, choose Garrus to lead squad 2.

There are other workable combinations, but this is what I used to get a "No One Left Behind" ending.