View "Survived Nightfall" for a good team set-up, I would recommend using it during a relic playthrough.
There are various ways to do this achievement. I would recommend doing this with a team of 4 people who have already beat Nightfall at least 1 previous time. Next, I would recommend having only two players using a relic at a time, and then switching and playing through a 2nd time. Having all four players with a relic could prove dangerous. If doing this with a good team of 4 players, two players should be able to use the "Take More Damage" relic while still being able to get through the level.
If you're doing this with a team of four players that will be taking turns getting the achievement, I would recommend that someone pairs the engineer class with "Smaller Wallet". After upgrading the engineer class to level 5, your wallet will hold $5000 which is still a good amount. You'll also be able to easily earn a good amount of money with traps and other kills. Another option when taking turns is that one player uses "Mortal" (No class selection). Based on the set-up in the screenshot above, it would probably be best if the ammo-supplying medic used this relic.
I do NOT recommend the "Pistol Only" relic for the Nightfall map because it is a lot harder than Point of Contact and is based more on offence than defence. The sentry has also been updated to reduce its power. Also, "Do Less Damage" isn't recommended either as you need as much fire power as possible.