Large family shoot - help

I just registered on the forum and have some questions on doing a large family shoot. I do not consider myself a professional by any means. Photography is a hobby (I'm actually an accountant by day). Please be kind

Some info:

I have a Canon Digital Rebel XT 8MP Digital SLR Camera with EF-S 18-55mm f3.5-5.6 Lens, Sigma 55-200mm f/4-5.6 DC Telephoto Zoom Lens, Canon Speedlite 430EX II Flash, Canon EF 50mm f/1.8 II Camera Lens and a Canon Wireless Remote .

The family I will be shooting is my own. My husband's grandparents are celebrating their 60th wedding anniversary. There will be 18 of us in the Outer Banks for a family beach vacation. We want to take photos of the group as a whole and of smaller family groups. These photos are very important as my husband's grandma was recently diagnosed with an aggressive form of brain cancer. My mother-in-law was going to hire a photographer, but with Grandma's health in bad shape, they thought it was best as we be flexible and see what days she is feeling the best to take photos. They asked me to take the pictures and I have agreed, but I want to make sure I do a decent job.

Based on what I have read, it seems the best time of day to shoot would be evening? This may be difficult with my 18 month old neice. How long before sunset is best? Does anyone have suggestions for posing such a large group? What lens would be best? I'm thinking the 50mm would be good for increasing the amount of light but not sure how it will do with 18 subjects. I will be bringing my wireless remote and a tripod so that I may be in the picture as well.

Any suggestions on how to make this a successful shoot? Thanks in advance for your help!

I doubt you can fit 18 ppl in the picture with 50mm on a crop sensor, unless you step all the way back. I guess stick with the 18-55mm, your only wide angle. I don't think there is much variation with your equipment. Your 430EX is probably not enough to light up the whole entire group without some sort of modifier.

I guess you will have to use the sunlight and get some standard looking group picture. Not sure if you are at the East coast or West coast, just have your subject facing angled to the sun instead of directly or go under a shadow, like under a tree or something.

Shoot it at 6~7 pm, just before the sunset.

And then you can probably do some individual shoot with 50mm or the telephoto.