My personal preference (not canon law):
I think the wedding party should all be considered “sacramental witnesses”.
Marriage is hard enough even, with the graces as a sacrament. If taking it seriously, and getting proper spiritual direction ahead of time, wouldn’t one want to be surrounded by people that can attest to the readiness and serious marriage prep that the couple put in? Praying for them from the day of their engagement?
To stand there, as Godparents in a way, to witness to, stand by, and say they will support the couple in striving for heaven.
I couldn’t imagine it any other way. I’m not married or close to it, but I have one sister who admitted to not going to confession for 14 years (since she got married), and another one who left the church. Meanwhile, I have a few girlfriends who I mutually share my faith with and pray with. The friends are my pick to be my sacramental witnesses.
again, not canon law or church requirements…my personal preference