Using the file you gave me, I modified the Flap System to 6 seconds so I could see slow movement. It makes it easier for me to see what's going on, and you'll probably want some delay in real life on your flaps.
Next I went to Mix and added Mix 1 as Normal type.
Then I changed it to FLP > LAL and for fun purposes put rates at 50%/50%. I set them to 50% so I could see some movement but not too much.
I then set the switch to B and made it active only in the middle position.
Now with B in position 0, when I move the D switch I see the flaps move slowly but nothing on the ailerons.
If I move B to position 1, the ailerons jump to the up position. If I flip D, the ailerons come down in sync with the flaps and elevator returning to center.
Because there is no position of the flaps where they are truly at 0, the ailerons are always up a little. You need to adjust that with the Offset field on the Mix screen, or by mechanically fixing the linkage so that there is a position where the flaps are truly at center at the appropriate switch position.
Andy