My family including two 14 year old kids will travel to Europe next summer for a month. My sister usually comes along but this time we are not sure how to split the cost fairly. Usually we only bring our daughter and do a 2/3, 1/3 split this time we are bringing her friend also. We usually do a group expense pot in which we put $275 dollars in for every $100 she puts in. My sister is no longer sure this is fair because our daughter is older. I feel it's fair because being 14 she doesn't drink alcohol and my sister likes to quit a bit. I also feel that because my sister contributes nothing to the planning, my husband and I do it all she just shows up with her bag (by choice), we do all the driving, navigating etc.. when there, we think this counts for something. What would be a fair way to split this?