I'm not gonna read his spoiler because I like to imagine it's the greatest explanation of the show ever and I'm almost certain if I look at it I'll be disappointed.
basically the guy in the red jacket in the last picture is grunkle stan he's an asshole . His brother the guy on the left is a smart as **** guy that studies paranormal activities, he came to gravity falls because it has an assload amount of paranormal sightings. He gets trapped in some extradimensional portal long time ago before the show starts, and some time through second season I believe stan saves him.
who knows what the other brother has been doing in that portal...
it could be literally hell in there, hard to forgive someone who sent you there for god knows
how many years even if it was accidental.
23 5-4-3-22-22-9-6-10 4-9-3-17-16 10-19-1 14-19-6-5-19-25 10-23-4-15-2-19 A STUBBORN TOUGH NEW JERSEY NATIVE
18-15-12-22-6-15-21-13 1-23-5-10'4 4-9-9 21-6-19-23-4-15-2-19 FILBRICK WASN’T TOO CREATIVE
16-23-2-15-10-17 4-1-15-10-5 1-23-5 10-9-4 16-15-5 8-12-23-10 HAVING TWINS WAS NOT HIS PLAN
5-9 16-19 14-3-5-4 5-16-6-3-17-17-19-20 23-10-20 10-23-11-19-20 22-9-4-16 5-4-23-10 SO HE JUST SHRUGGED AND NAMED BOTH STAN
Some secret messages within the newest episode. Less than five days for the new episode, get hype boys.