Can they merge to pass phase levels? Could have a full voting process to ensure members don't double up. A lot of the proposals seem very much the same.
Multiple similar proposal are part of the process at area 51. For the most part there is a not an "official" merge process. People choose to support and post to the ones they like best, and it develops from there. If you post a discussion with links to all the related proposals it will show in the header of all of them, and bring awareness to all.