Every year I take a 300 mile ATV trip on a major trail that takes about 5 days to do and I' ve learned a few tricks. I don' t care how light you pack I don' t see how you' d fit gear for 6 people on one horse but you could probably pack gear for 2 or 3 maybe 4 on one horse. Heres what I do on my ATV trip.
1. Leave wall tents at home and get ready for roughing it a little. Pack a light weight, compact run of the mill camping tent. You can get a big dome tent for relatively cheap and it' ll sleep 6-8, not to mention a relatively light and small size.
2. Get backpacking stoves and a mess kit. Very small but can heat water and canned meals quickly. They also double as heaters.
3. Take your water filter cause you' ll save a ton in weight if you can do that.
4. What kind of food you take will be a big part of how much weight you save. I take a lot of MRE' s for lunches or midday meals. Take one or two canned meals like chili or something else so you don' t run your partners out of the tent at night.
The key though is take the smallest protion you can. Jerky is great as well as small treats like hard candy and rice crispy treats. Take a small cooler and pack some eggs and meats for dinner and a breakfast or two. In the cooler take some of the good stuff like milk, butter, salsa, ketchup and things like that but keep the portions small. I like to keep condiment packets from Mcdonalds and places like that. You know the little ketchup, mustard and mayo packets they have. If you look around you can get all kinds of stuff like honey, relish, butter, salt, pepper and bar-b-que sauce. KFC usually has lots of stuff like that. You can also take 4 or 5 slices of bread by putting it in a appropriately sized tupperware dish.
5. Get a " stuff bag" for your sleeping bag. Its a bag with straps on it that you tighten and makes your sleeping bag about half the size. For a little comfort you usually have room for a self inflating pad for under the bag.
As far as clothes you' re on your own to pack light but you can save a lot of space there too if you do it right. Remember buy everything small from your water kettle(mine was $2) to your tube of toothpaste(99 cents at the grocery store). The amazing thing is that it really is not very expensive to stock up on " the little things" .