Yes 550D can use the 24-70 but it's not advisable as 24 x 1.6 = around 40mm, which maybe too narrow sometimes. If you want the 2.8 aperture, I recommend canon EFs 17-55mm 2.8 with Image Stabilizer. The reach is just right and IQ is similar to 24-70.
Like what alwaysjerricky had mentioned, 24-70mm (EF mount) can be used on the 550D, but it might not be the best lens to use, depending on how you want to frame your photos. On a crop sensor camera, 24-70mm is not really that wide.
No, you need to get a white lens for weddings.
Jokes aside, any lens that you are able to use will work. Kit lens, UWA, prime, zoom, you name it.
If you think that it needs f/2.8 then read up again about DoF, use a calculator and do some checks. Family members are not interested in thin DoF experiments. They want to see all aunties and uncles in group shots around the table. For this, f/5.6 and flash works best.
If you search the forum you will find similar threads and the recommendations are all the same. Lenses don't make wedding pictures.