Just my humble opinion, but:
Whatever you play keep things 'up', people are trying to party, they've just listened to a crock of speeches and they want to dance to let off some steam. Don't be tempted to play some dark droney stuff even if its requested What are the guests supposed to think about some song about a suicide? Radiohead are not a wedding band! Remember that.
You prob have a few different age-groups there, so maybe go for broad brush strokes to get things going. Van the man Beatles & Stones at some point, maybe some kinks or 60's 70's rock. You Never Can Tell by Chuck Berry is a good easy one, because its only two chords and is a lively track on the right subject.
If you have only got a few songs make them all good and then sit down, the dj should do the rest.
For some weird reason when we play weddings we are almost always asked to play Mustang Sally, I have no idea why, but people do like it, also Sweet Home Alabama and I'm a Believer. I draw the line at Summer of 69, because I start felling sick as soon as anyone mentions it, but it seems to be really popular with some people.
If you are not from that sort of family, why not chat to some of your sisters mates and find out what she listens to, and try and learn one or two requests.
Good luck, don't bore them