I was in a similar position a few months ago. Asked by family to do a wedding. Th bride is a newly finical adviser and the groom a still in school accountant. So I warned them in advance, i hadn't shot a wedding in 25 years, didn't have any flash equipment, and couldn't afford to buy equipment just for the wedding. I shot the whole wedding with my Sigma 70 macro 2.8 (rings, bouquets and some ceremony images), my FA 50 1.7 was the workhorse, and a few 200mm images from the balcony, and by a few I mean, not really worth bringing a lens for. I needed my DA 35 2.4 for a few images and didn't have them and shot almost everything with the K-1. So maybe a 35 and the 21 and 50 macro if shooting APS_c .
What I did was I get there a day early so I could go to the rehearsal, took 20 or 30 test shots, so I was comfortable in the nvenue. Even though the lighting was the worst I've ever shot in, things went well.
As for getting in t he way, I did it constantly. The only time I floated around the outside was during the ceremony itself.I moved into the isle as the parties came down and held up my hand to stop them in place, then gave them a thumbs up when I finished.
Here I am,