I'm going to assume, charitably, that Kate picked a fairly meh dress as an act of kindness, so that she wasn't upstaging the bride. It was probably the only way to miminise the inevitable attention that she would get.
Fergie has chosen her daughters' stylist? Bit like getting Helena Bonham Carter to pick your outfit for a big night out, surely?
"Why is Zara not a princess? All the other grandchildren seem to be. "
Because she is not a member of the male line and Princess Anne refused an honory title for either her or Peter.
"The maid of honour was her best friend Dolly Maude and the little page boy was Ted, Dolly's son and Zara's godson, as for the other bridesmaids I'm not sure"
from a news report
"Zara Phillips beautiful bridesmaids were Stephanie Phillips, Miss Phillips's half-sister, the daughter of Captain Mark Phillips and his second wife Sandy Pflueger, Nell Maude, Jaz Jocelyn and Hope Balshaw."
Nell Maude is Dollly Maudes daughter and Hope Balshaw was the best mans daughter.
So they do seem to be managing the blending of the families, with the legitimate half-sister as bridesmaid.
I saw pix of the Princess Royal and Capt Mark Phillips with Mr and Mrs Tindall - so looks as it the "exes function as parents" rule was the one that held good. I didn't see anything of the second husband and second wife.