This is what I think how Life is Strange 2 is going to end; because the assumption is that we will NEVER get a happy ending; no matter the choices made.

In Episode 4, Sean probably gets out of whatever predicament he's in (if the Episode 4 teaser is any indication that things will turn out bad for him) and reunite with Daniel; though their relationship will be greatly strained due to the latter apparently abandoning the former. In Episode 5, the siblings will probably find their mother, but the cops will somehow find out too. The mother will probably get killed on accident by the cops when she tries to defuse the situation; causing Daniel to lash out and prepares use his powers to kill the cops because he'll believe that all cops in the United States are above the law and that they ultimately decide who lives and who dies; apparently just like with his father. With this mindset, Daniel believes with his own power, he should do the same to the cops and he kills every single cop except one who would manage to call for backup. Before Daniel can kill the remaining frightened cop, Sean would be left with one final choice: "Stop Daniel" or "Kill Daniel."

Stop Daniel: Sean attempt to persuade Daniel to stop, but the latter refuses to listen and uses his power on Sean because he believes that Sean has always held him back since the beginning; which results in Sean's death. Daniel would then fully embrace the darkness within him and kills the remaining police officer. Sometime later, the police backup arrives and Daniel looks at them with an evil grin and kills them off-screen.

Kill Daniel: Sean takes the gun of one of the cops that Daniel kills and tearfully shoots Daniel from behind before the latter can kill the frightened cop. Realizing what he has done, he goes into a mental breakdown as memories of the entire journey flashes in his head. Realizing that his entire family is gone, and with nothing left to live for, Daniel succumbs to despair and then points the gun at himself and takes his own life. Because the remaining cop survives, he is able to tells the news reporters what really happened.

The rest of the ending would probably be the surviving characters reacting the heartbreaking news; with those knowing the real truth realizing that the siblings would always be sadly viewed as the villains.