The Texas Chain Saw Massacre

This achievement is mostly dependent on luck, you have to play as a Family Member and pick Sissy, use her poison breath ability to leave a poison cloud and hit 2 victims with it, they don't have to be poisoned at the same time as long as they are affected by the same cloud, there are some things you can do to maximize your chances:

-Level up your ability tree and unlock longer duration clouds.

-If you know which basement exit is being opened try to place a cloud in the stairs and with some luck 2 or more survivors will just run through it.

-Have friends helping with their ability and good call outs, Cook and Johnny are perfect for this as their abilities help you track survivors.

-Pay close attention to which exits are being unlocked by the victims, if they repair the Fuze box or the valve immediately run to that exit and place a poison cloud, leave some ground for the survivors to reach the exit confidently and approach them so they escape by running through your cloud.

-If you face a toxic team oftentimes they will wait on one exit until you come close, if you are lucky they will stay just enough time for you to get close enough to use your ability.

A pretty easy way I found to get this is when the Victims have powered up the fuse box exit, plant a cloud in front of the doorway. They won't hesitate to run through it because the exit is right there, so getting two people poisoned is very easy this way.

Hope this helps!