Goodness janer, I can't begin to imagine your friend's state of panic, never mind her DD's and SiL's !!! A twin pregnancy was one of my DD's greatest fears, being a single mum. Her relief at her first scan was palpable when the sonographer said it was a single embryo. She kept saying, "are you sure? Really sure? Oh thank God". And then burst into tears.
Nelliem what a fun idea that is!
Re button bands and sewing up, I just found this pattern on Ravelry for a little crossover cardigan which is knitted sideways - all the bands are knitted with the main body, so NO picking up stitches anywhere. And the only sewing up is the side and sleeve seams!