Should I Save Joe and Jack?

Whether to help Jack and Joe in Dying Light 2 or not has far-reaching consequences. You're still free to give the tower to the Survivors or Peacekeepers no matter your choice, but a later quest will change drastically depending on what you do with the murderous pair.

What happens if you save Jack and Joe?

If you choose to help Jack and Joe, you'll later find them within the Peacekeeper's massive ship base. Meeting them there later in the game lets you have access to an extra side quest, so this generally is going to be the best choice you can make.

Should you let Jack and Joe live?

They aren't powerful, but since there are two, you'll need to isolate one and use some strategy to win the fight. Killing them will also give you control of the water tower. Again, it is entirely up to you to make the decision. Helping them is the subjective best choice, though.