Q: What do you recommend re: concelebrants at weddings?
I would say that the presider does all… but, analogous to the deacon situation, may a concelebrant (assuming he has the faculties) witness and receive the consent?
A: The Ceremonial of Bishops presumes a situation where a concelebrating priest assists a presiding bishop (602). Before the post-Vatican II marriage rite came out, Inter œcumenici envisioned an assisting priest in alb and stole, perhaps a cope (72). The presider was to give the blessing of the bride (now called the nuptial blessing). These distinctions have fallen away. In theory, a concelebrant could preside for the wedding and not the mass, but I think it makes more theological sense for the presider to preside for the wedding, and it makes more liturgical sense for the presider to give the nuptial blessing. But we have no rules on this.