This sounds like a lot of fun!
Regarding food, I married into a large family so we have a lot of LARGE functions. You can throw together a green salad or fruit salad pretty easily and that fills out any of the options below. Barbecues are always relatively easy, as the meat comes basically prepared. I also make a salad with the ratio 1 can black beans, 1 can corn, 1 red bell pepper, tomatoes, 1 avocado, a handful of cilantro and a dressing of 2 crushed garlic cloves, 1/2 c red wine vinegar, 1/4 c olive oil, salt and pepper to taste. For breakfasts, you can cut up a fruit salad and make some quiche (these freeze well) and scalloped potatoes (low prep if you have a cuisinart). Another option is to buy rolls and get a honey baked ham. Monkey bread is easy and pleasing, if you fake it by taking pillsbury biscuit dough and dipping balls of it in cinnamon and sugar and butter then stuffing these in a bundt pan. We do "mexican" as in tortillas, black and refried beans, cheese, jalapenos, grilled onions and bell peppers, grilled meat/shrimp, sometimes mango/avocado/onion/jalapenos/splash of cider vinegar/cilantro, chopped chipotle peppers, and a selection of hot sauce. The key with Mexican is that it is so simple you can go crazy with the options and that is the fun part. We've also done greek with pitas, basil, falafel balls (you can get a mix and bake then freeze these), hummus (variety) and babganosh- STORE BOUGHT!, cucumber/yogurt/dill, yogurt with 1tbs tahini and a ton of garlic, kalamata olives, feta, tomatoes, lemons, you might make some lemon chicken or something on the grill... All of these are relatively easy to prepare or can be prepared ahead of time. The key is simple! You can spice up a green salad with cranberries, goat cheese, nuts and a vinaigrette or fresh green beans, tomatillos, bell peppers, and avocado or pear, walnuts and goat cheese with a vinaigrette... Never under estimate french rolls, lunch meat, and a selection of cheeses like brie (with roast beef), swiss or gruyere, and the standby cheddar with a store bought or handmade fruit plate. Costco is a life saver these days with their giant cheeses and great fruit and veggie plates. If you've got platters and can get ahold of some berries, kumquats or a few pomagranites, you can make THEIR platter look like you slaved away!
If you can tell, I'm all about food.
Regarding genealogy, I love the idea of drawing a tree on butcher paper and having the family sign in what they know. I also think it would be great to have a polaroid and a hand drawn tree and post pictures on the branches... too bad it is hard to find those polaroid stickers these days... We set up a download station at our wedding where we bought a universal card reader and asked people with digital cameras to download their pictures to add to the wedding album. We got a ton of great pictures this way. (and a lot that people probably didn't expect to give us, but that we enjoyed like water skiing pics!) That would be great for you guys at the end of the weekend, and then you can either post pictures through something like picasa or you can burn cds of pictures (or have costco or someother such place burn some for you...)
It is relatively easy to capture the moment in t-shirts from cafe press.
If you can't do a family campfire with ghost stories or stories from the "elder's" childhoods (as those are a blast!), a fire pit is fun.
Martha Stewart had a movie party for a kid's birthday party where they had a bunch of old fashioned candy, popcorn and rented a projector to show a movie on the wall of a house... I've been wanting to copy this.
Hope you have a great time.