I live here on Alderney and can advise on restaurants etc.
The Harbour lights is OK, chef has changed recently but I haven't heard anything good or bad!
The number of you does limit things, but there is time to book something up.
The Thai and the Indian both have big enough tables for you, both are very good but I guess you have enough of those back home!
Not sure if you are aware but Bumps moved up into town, behind the Indian. Good food still and a nice outside eating area.
The Georgian could get you all easily in their restaurant, The Orangery. Very good gastro pub type food and the liveliest pub in town. Also has the advantage of good draught bitters, lagers and Guiness. The other establishments mentioned so far, except the 'Lights, only have bottles & cans.
Where Bumps used to be in Braye St is a new restaurant called Cantina No6. Only been open a week or so but reports are good. Also has a small selection of draught beers I believe. Not sure if they can take a big party though.
The Braye Beach could fit you in but it's all 'Nouvelle Cuisine' and bonkers prices!
Hope this helps, and fire away with any questions!