Right, with all your help I think I've figured this out now. The best way to make the 9-patch is to use the picture fabrics top left and bottom right and the other non-directional fabric top right and bottom left. Then doing the swap described above gives me the D9P block with the pictures the right way up. I was trying to do a 9-patch using 4 pictures, then another one using 4 squares of the second fabric, which won't work unless I change the direction of some of the pictures.
Thankyou - I knew I'd get my answers on here!