Let this be the rows of chairs:
[] [] []
[] [] []
Let their be siblings x and x, y and y, and z and z. Beginning with placing the x siblings, there are 6 options for the first sibling obviously, and 4 options for the second sibling, giving us 24 ways of placing them (6*4):
[x1] [] []
[x2 not allowed] [] []
Let's say we go with this arrangement:
[x1] [] []
[] [x2] []
We must place one of the y siblings in the rightmost column, or else the z siblings will be front and behind each other (there are two ways to do this):
[x1] [] []
[] [x2] [y]
Then there are two ways of placing the other y sibling (row 1 column 2 or row 2 column 1), giving us 4 ways of placing the y siblings (2*2), but then we could also swap it so that sibling y2 could be in the right most column and y1 is in the other spots, givings us 8 ways of placing the y siblings:
[x] [] []
[y2] [x] [y1]
And then the z siblings go in automatically, with 2 ways, as we can swap z1 and z2. this gives us 24∗8∗2=384 ways. Sorry if my explanations a bit long, this problem I found hard to explain without going super in depth.