With some guidance from Roisin I was able to merge the two patterns by making myself the dress in the middle out of some old fabric of my grandmothers. I cut a 8/12 bodice and a 12 skirt as per the pattern and sewed them together. I did not modify the bodice, but then marked onto the skirt where the pleats needed to move to, then took out the basting and modified my pattern. My other pattern changes were to bind the neck and arms in bias binding, and to lengthen the skirt by 4 inches (which is much too long).
I have now measured up two of my three bridesmaids (my sister is getting a break right now as she is in the middle of exam study. I made muslins of the the bodices for M and K, and then using their chosen fabrics sewed up these dresses. They are now waiting to be tried on once more to confirm skirt length.
M and K are my best friends. We have known each other for years, going right through school together. M and I have been best friends since kindergarten, and K and I since high school. We now all go to university together (completely unintentional) though we are all studying different things. It's been so exciting making these practice dresses for them, as they are both so stylish, and they suit them perfectly. M's dress is the red dress. She wears a lot of red, but assures me this one, with tiny brown and green flowers, is different to her five or so other red dresses. K's is the blue one, and is a brilliant party dress; it has already been earmarked to wear to two weddings this year.
Doing this process has taken away any nerves I might have had about the actual bridesmaid dresses. I am looking forward to making one for my sister, it might end up as her graduation/formal dress, or we may go the hippy route... who knows. There is just something so nice about sewing for other people.