Originally Posted by
akolaw
The two boys stand by relationship not logic, they have argue whether they should stand by Susu, their sister or Li their brother, and they decided to stand by Susu because they know Susu a few hours earlier.
Some times we made our decision not by our brain but by the position our butt sit on, in this case that is the option the two boys made. They adopt Susu as sister, and treasure her as such, and they do the same to their two adopt mothers.
Chinese have some unwritten rule about how one should treat their family, sifu, adopted brotherhood etc. which may or may not agreed by modern society.