Been there, done that. They won't look at you as a professional so getting really great photos that a pro would get for a stranger is next to impossible. You wot enjoy the festivities, the cake, the company because you will be too busy snapping photos. Then, how on earth can you charge your friend for the photos. I would agree, give them a credit towards your services or recommend a professional and offer to be an adviser if needed, but don't do it
it's not worth the headache before, during or after.