My second wedding, twin daughters (18) who stands next to me?

My wedding day is coming up (6ish weeks). I don’t know what order to put my kids in for the wedding ceremony. Our six kids will be the only attendees of the wedding party. We have only family coming as guests, 35 total.
My twin daughters just turned 18 and I have a 13 year old son. My fiancé has three kids as well, son (29) and two daughters (14) and (12). The oldest of my identical twins (by three minutes), has put herself in the “backseat” a lot because her twin sister is a bit dramatic. The drama comes from depression and low self-esteem. As they were growing up I made it a point to make them both feel special. For birthdays we would take turns, even and odd birthdays, with who we sing to first. For my wedding, I can’t decide what order to put the kids in for the ceremony. My fiancé will have his order be; his son, older daughter, then younger daughter standing up for him. For me, I’m not sure. I’d like to do age order but it’s a bit tricky (I think). My oldest isn’t able to help as much as the youngest of the twins. Basically, someone has to stand in the middle. Who?