Well again SPOILERS!!!!
It's actually not that hard! if I remember correctly you need to fight/push away the hand that grabs you while he is bound up because then u will get the opportunity to free him instead of leaving him behind.
After that u have to choose to let him stay with the group of course :)
And idk if u managed to do that but if you'd know how to save the uncle aswell I'd appreciate that! Didn't know he could be alive aswell cuz he died for me..