We have broken our costs down into several parts. Carrying Costs are the things that have to be covered to maintain the value of the home. These are also the things which (to a large extent) continue to be expenses whether or not everyone is in residence. Everyone pays these expenses even if they are away from home for a month or more. We can't turn off the heat just because one person is away!
Food is a different story. Each of us only contributes to the food budget for the weeks when we are home.
In addition, for the first couple of years, we will all contribute to a joint savings account that can be used for maintenance in the longer term. For example, at some point down the road, the roof will need to be replaced. But once the contingency fund is a reasonable size, we can stop contributing to it until it is depleted.
Monthly Carrying Costs (heat, hydro, taxes, etc)
We still don't have our new property tax assessment, so this may change. For now however, we each contribute $1100 per month to cover carying costs. This is more than enough right now. Like anyone who moves into a new house, we have had a lot of expenses for small additions, bits of maintenance work for changes we wanted, etc. The actual carrying costs (with the old tax assessment) is under $2000 per month.
We have been pleasantly surprised by the cost of heating the house. It really pays to have a well insulated house with a high efficiency furnace.
For now, we are all contributing $100 per week when we are home. As we shop, we reimburse ourselves from the "food pot". It's working well. For the most part, we seem to be shopping for the main meal each day. No one is "scheduled" for any particular day, but we figure out who is going to be home for any given meal and then someone volunteers to shop and cook. The others clean up! Breakfast and lunch are usually meals we fix for ourselves, but sometimes someone volunteers to make something special.
We think there are other savings to be had as well. We probably only need one or two newspapers. Magazine subscriptions might also be shared. It's even possible that eventually people might decide that a couple of shared vehicles makes more sense than everyone paying for maintenance on their own vehicles. At some point, we may want more in-house services - like an accountant, a regular housekeeper who also prepares meals, etc. That can be worked out as the need arises. But again, if you divide the cost by four, some of those services may seem pretty affordable. See an example for caregiver costs.