the Sully kids' reaction to Jake saying Spider "knew everything" breaks my heart.
they knew him better than anyone else, better than their parents. they knew his love for Eywa, for Pandora, for The People, for the clan, for their family. they knew he would never tell the RDA anything... not willingly at least.
they knew they were leaving because Spider would be tortured for information, he'd be forced to reveal their home, their plans, their numbers, their weaknesses. their brother would be tortured and they were being forced to leave him behind.
they knew they were being forced to find a new home, without their brother, because their dad knew he would be tortured.