Best Man
The Groom's personal body guard. Would gladly take a bullet for the groom any day of the week. As long as the bullet is a marshmallow, aimed at the mouth. Also they worked a security job together.
Maid of Honor
Sister by choice, not by blood; grew up running around the woods with the bride and playing "spies" against siblings.
Groomsman
The Groom's personal accountant. Launders the money for all of the groom's illegal activities (or would, if the groom had any...).
Bridesmaid
Comrade in arms; Always made sure bride was equipped with pink Crocs and stylish PJ's during times together in Iraq.
Groomsman
World's most advanced Artificial Intelligence, designed by the groom to be the perfect friend and disguised as a real human under the backstory of "Bride's little brother".
Bridesmaid
Spent teenage years as bride's #1 partner in crime. Best person to torture for insight on bride's inadequacies and weaknesses. (But the answers are social skills and beef jerky, so you can skip the torture).
Groomsman
"The Cleaner" whenever the groom goes on a murderous rampage. So good at his job, even HE can't find where the bodies are. Also they went to school together.
Bridesmaid
Female soul mate and most probable culprit if bride ever goes missing under suspicious circumstances.... Met at dance school as teenagers and bonded over mutual weirdness.