I happen to know of an unfortunate story where somebody’s son became unobservant, and a well-known (and knowledgeable) Rov was indeed mesader his Kiddushin. Not sure why though.
As for the chosson and kallah making the brachos, apushtayid has supplied a source (the Aruch HaShulchan) that somebody other than the chosson and kallah should do it, and as GAW pointed out, having both of them make it is certainly a bracha li’vatalah.
Not sure what more we need…