After watching some rare interviews, the point of the Garcia family (Mostly) is for Clementine to discover an actual functioning family that is still alive and work together. The synopsis of season 3 is that how far would you go to protect your family? When Clementine meets the Garcias, she is surprised that this family actually works, they don't fight each other, they work together to survive and there is no option for Javi to say....kill David after he attacked you because he is still Javi's brother. The point was for Clem to discover that family can work in the apocylpse. Kenny lost his whole family, Lee also lost his family, Lilly's dad died, Alvin and Rebecca die no matter what but AJ still lives. At the end of Season 3 Javi still has family in the form of either: Kate and Gabe, Kate (Romanced) and Gabe, Kate (Romanced or friendzoned), Gabe, or Gabe and David. This helps prove to Clem that family can work in the Apoclypse and so she gets a family with AJ and then the School survivors in Season 4.
I got all this from the Interviews regarding what Season 4 is gonna be like after Season 3 just ended.
(For the record, David is a jerk because of his PTSD from his time serving in the army, he is a good man it's just that the army messed up his personality which made him difficult but deep down he is a good man doing what he thought was best in a bad situation)(Kate caused nothing but trouble, she started the whole David and Javi fight in the first place for no reason but to make David mad and she was the one who wanted to leave Richmond even though that caused trouble with Ava, David and Gabe's realtionship with Javi)(No comment on Gabe).