Two brides, that sounds awsome!
Can I ask why you are wearing a dress too Ethan? Or is it you as the collective you going to be wearing the dress i.e. this is not just a marriage between Ethan and Adrianna but a renewel of vows between adrianna and all of you?
Sorry, just curious.
I think you can go as complex and simple as you like. There is nothing legal involved in a vowel renewal so you don't need a celebrant(though one could definitly help). You could always get some other person you both know and trust to facilitate, a mutual friend for example. Usually these things are really simple, between the couple and close friends and family, less formal or costly than the big shebang.
If it is just not you Ethan, then maybe other personalities would like to have a say too? That would be cool I think.
You could play on the 'classic' wedding - have two brides on the cake, a bevy of brides maids, two best ladies, etc..