I think the pictures are not clear.
Parts 12 and 13 are the bottom trims that clip to the underside of the door.
I think original poster is talking about the strips that adorn the middle of the door, halfway up.
I cannot see where parts 7 & 8 would go either.
Here is part 1 and most of part 2;
And here shows parts 1, 2, 3 and 4
Note on this picture, parts 12 and 13 the bottom trims on the door are removed, as is part 2 on Mmmfive's post picture the main bodykit sill.
I don't see where the two parts 7 and 8 go, unless they are behind the wing and rear arch and bolt/screw onto the chassis providing a base for parts 1 and 4 to clip on to?