Don't be surprised at how much the universe can change by the end of Mass Effect Legendary Edition. This is, after all, one of the game's best selling points. Player choice is the number one draw to the franchise and these choices have lasting changes on the individuals and even the societies within the game's plot. Nowhere is this more evident than the Zhu's Hope colonists on Feros.
However, unlike the other instances of player choice, which are done through dialogue options, this choice must be made on the battlefield. And it's not exactly a simple choice or "shoot this, don't shoot that," either. These characters will appear in the rest of the series unless their lives are snuffed out here. So for those looking to make lasting relationships, here's how to save their lives.
The Proper Preparation
After going through the ExoGeni base, get back in the Mako and head out. A cutscene will force Shepard and the squad out of the Mako. After this interaction, speak with Juliana Baynham before going back to Zhu's Hope. She'll give Shepard a critical mod.
Be sure to load the Anti-Thorian Gas I mod into Shepard's grenades manually as it will not be automatically equipped. The description is unclear, but this must be done otherwise the grenades will be fatal against the colonists.
Proceed to Zhu's Hope with the Mako. Just before entering the colony area, a brand new unit, the Thorian Creeper, will attack. After this, a dialogue box will pop up. Neither selection is marked as paragon or renegade, but the implications on both are huge.
Players must select "Careful. Leave the colonists." If they choose "Wipe everything out," then the squad will shoot civilians on sight, well before when Shepard can use the non-lethal grenade. Save the game before opening the garage, just in case a civilian gets killed.
Pacifying The Colonists
There are two types of enemies here. In the simplest terms, the Thorian Creepers can be killed, they do not count as colonists. But any other target or enemy counts as one of the sixteen colonists that needs to be saved.
The Anti-Thorian Gas is deadly and will kill Thorian Creepers in one hit even on the Insanity difficulty, but it's recommended that players save their grenades for only the colonists. Keep in mind there are sixteen colonists and even with the full amount of grenade upgrades, there isn't enough. Try to knock out at least two colonists with each grenade.
The radius of the grenade is much larger than expected. For example, all four shooters in the first room can be pacified with a single blast. This can be hard to do when under fire, so use Biotic Barrier or Immunity to negate incoming fire from the friendly units.
Repeat this process until back at the beginning. Congrats on saving so many lives, commander!