So you are near the end of episode 5 and David has just fought with you (even if you played the game anti-Kate/pro-David but whatever). He then storms off with Gabe and you must choose to either go after them or help Kate with the Richmond walkers. Javi will go wherever you choose to, while Clem's choice depends on a variety of factors. Both Javi and Clem's choice will decide which of Javi's family lives or dies. This guide will explain how to get each ending.

While you the player can choose to either find Gabe or go with Kate, Clem's decision is based on the choices you made as her in the EP2 and EP3 flashbacks (the ones with Ava and David's camp respectively). Clem's choice depends on whether you:

• Accepted Ava's offer to join the New Frontier (Clem's EP2 flashback)
  
• Gave AJ the medicine (Clem's EP3 flashback)
  
• Spat in David's face (Clem's EP3 flashback)

Based on various combinations of these choices, Clem will do one of the following:

• Follow wherever Javi goes
  
• Follow wherever Javi doesn't go
  
• Follow Gabe regardless of what Javi does
  
• Follow Kate regardless of what Javi does

Here are the possible actions Clem will do depending on the EP2/EP3 flashback choices

• Accept Ava's offer + give AJ medicine = Clem will follow Javi
  
• Accept Ava's offer + don't give AJ medicine = Clem goes after Gabe
  
• Reject Ava's offer + give AJ medicine = Clem goes where Javi doesn't
  
• Reject Ava's offer + don't give AJ medicine = Clem goes after Gabe
  
• Reject Ava's offer + give AJ medicine + spit in David's face = Clem goes with Kate
  
• Reject Ava's offer + don't give AJ medicine + spit in David's face = Clem goes where Javi doesn't
  
• Accept Ava's offer + give AJ medicine + spit in David's face = Clem follows Javi
  
• Accept Ava's offer + don't give AJ medicine + spit in David's face = Clem goes with Kate

Source:
https://www.reddit.com/r/TheWalkingDeadGame/comments/6efwgg/spoilers_how_to_influence_clems_final_decision/

How to get: Follow David/Gabe while Clem does the opposite choice or just chooses to go with Kate.

Description: Javi is able to track down David and Gabe's truck by himself. He is able to save Gabe, though David has been bitten and is put down by either Javi or Gabe. Javi and Gabe then return to Richmond to help out Kate, however she isn't found through the horde and is presumed to be dead after 3 days of searching (this was the ending I got).

Alive: Gabe
Dead: David, Kate (technically she's missing)

How to get: Choose to find David/Gabe while Clem agrees to go with you or chooses to find Gabe.

Description: Javi and Clem are able to track down David and Gabe's truck. They are able to save both Gabe and David, who have NOT been bitten. David decides to leave Richmond by himself because he knows that Kate doesn't want to see him.

• If Javi tells David to leave, David will do so and his status will remain unknown.
  
• If Javi tells David to stay, David will stay in Richmond and he will be alive.

Javi and the rest of the group return to Richmond to help Kate. However, Javi spots a zombified Kate and can either put her down or let her roam.

Alive: Gabe, David (or determinately unknown)
Dead: Kate

How to get: Join Kate in Richmond while Clem does the opposite choice or chooses to find Gabe on her own.

Description: Javi joins Kate in Richmond and is able to seal the walker opening along with Jesus. Clem returns with Gabe who says that David got bit and had to be put down. Javi and Kate later find David's dead body.

Alive: Kate, Gabe
Dead: David

How to get: Join Kate in Richmond while Clem agrees to join you or help Kate on her own.

Description: Javi, Clem, and Kate are able to stop the zombies along with Jesus. Javi and Clem then find David's truck to find a dead David and a bitten Gabe. After a tearful farewell, Gabe is put down either by Javi or himself.

Alive: Kate
Dead: David, Gabe

Bonus: Depending on your S2 endings, Clem will give Gabe a different type of farewell:

• Jane = Clem kisses Gabe (AKA the dark timeline)
  
• Kenny = Clem hugs Gabe
  
• Alone = Clem holds Gabe's hand
  
• Wellington = None of the above

https://www.youtube.com/watch?v=k0N6ut5_psA&feature=youtu.be

Each of these endings results in some altered dialogue after the fighting is over, and you'll be able to see who is alive. It's unknown how saving each person will affect the future, though knowing TellTale they'll probably just kill the rest of Javi's family in a car crash flashback.

EDIT: With The Final Season now over and the series presumably concluded, it should be noted that none of these endings have any effect in the final game. Take that as you will.

Hope this guide helped those confused on how to get these endings. Special thanks to reddit user /u/SwixSwax for their info on how Clem makes her choice.

Also as a bonus, here's a really long non-canon death in episode 5:
https://www.youtube.com/watch?v=VYalU-bHDio