In September of last year, my extended family went on a joint vacation. Since we traveled from different places, we only split the cost of the vacation home we rented.
It was: mother, father, myself, my DH, my DS, my sister1, her DH, and sister2. To make it fair and even, the cost of the vacation rental and fees was split 8 ways, and payment was due to me (I paid for the whole thing) 6 weeks before. Everything else was piecemeal. We took turns cooking, with each couple taking a few meals. It worked out well, and the only glitch is that not everyone wanted to go and do everything, so it was great that we had 3 vehicles as we were an hour from the closest town.