You tired calculating who owes who after an event ?
Use this application. Simply create a trip (or any other activity), then add individual expenses for it. From there, you can add the parties involved in that activity and how much each person contributed thus far. Then the app does its magic and figures out each person's current balance, as well as who owes what (and to whom) at the end of the event.
With Family Sharing set up, up to six family members can use this app.