when siblings are from the same two parents, they are sorted on the tree view according to their birth sequence. The oldest is on the left and the youngest is on the right.
For some reason, if for example, there are two mothers, then the sorting is always mixed out so the children from the second mother will be on the left side and only then there will be the oldest siblings from the first wife.
I think that children that the children from the later wife should be on the right hand side to avoid confusion.