Two things I've learnt over time (and try to stick to) are:
1. Try not to be in the face of the family the whole time. In particular for an official / religious ceremony taking photos from the side is less intrusive to the participants, but there's another benefit. You're there to record the memory... having a cheesy snap with everyone smiling at you during the ceremony looks false and will only annoy the family and ceremony official - showing them really enjoying the moment is a much better memory. By being a little to the side you have more time to frame the photo and can make sure the shot is completely natural. (Needless to say you need to take both candid and posed ones).
2. Ask the ceremony official and the main participants to give you priority for the group poses. More often than not there will be lots of people with cameras at such events (often several semi-pros who are thinking the same way as you in terms of what shots to take). You all want the best shot but don't want to have eyes in different directions, smiles missing etc. By taking it in turns it becomes easy. The problem can be the family member with the compact who doesn't follow the same rules. That's where getting everyone to know that when you are taking a photo they should look at you makes a difference. I also tend to ask the ceremony official to announce it at the end so that people know they have to give a little bit of space... ceremony officials by nature are cautious of photographers for getting in their way, but if you stick to my first tip above then you'll be in their good books and they'll happily ask you are given that little bit of space.
Anyway, here are some photos from this particular special day. Sharon and Ricardo had a great time with their twin daughters Eva and Marina and needless to say gave me permission to include a few of the images here (a point I tend to blog about a lot!).