You might also ask first if they are happy to have the photos just as they are. They may not want any special adjustments.
Otherwise, for a full-length shot, you can shorten him by having him stand behind her about one step (adjust the distance as necessary) and shorten his torso into his hips (sort of a slump), and lean in toward the camera. He can keep the visible leg straight toward the camera and bend the one hidden behind her body to lower his head and shoulders even more. Just watch that you do not create a shadow across her face and that his shoulders remain square.
If her dress is long enough, or has a train, you can stand her on a small stool or small box and then position/drape the dress and train around the front of the stool to hide it.
If you have a ladder, put
yourself on the ladder so that the camera is close to or on the same plane as the groom's head. If you have to tilt the camera up to get him in the photo, he will just look even taller.
You can also take a nice 3/4 shot looking
down on both of them from above. Put yourself on the ladder so they can
both look
up at you. Then put her on a stool or box to bring their heads closer to level, but let him put his arm around her or let her lean her head into the area between his chin and chest for a more intimate and romantic pose.