I jointly own a property with two of my sisters. When we purchased the property I put a £10,000 deposit down and was the sole contributor to this. All three of us are currently paying one third of the mortgage payment each.
One of my sisters is now moving out and I am going to be picking up her share, so paying two thirds of the monthly mortgage payment from this point forward, and we are hoping to sell in approximately nine months.
How do we fairly work out our individual shares to take into account my increase in mortgage payments, and the reduction in my sisters'? Thanks.
Update (incorporated from OP's update-posted-as-answer):
I am happy just to get my deposit out with no interest on that. I am close to my two sisters, so there is no argument over the deposit. Also, we did a deed document at the time of purchase to say that I would get this deposit repaid first.
After payment of the mortgage, the deposit, and other associated costs, we think (based on a recent valuation) that there will be an additional surplus of £12,000 to be split between the three of us. However, if I do end up covering one of my sisters' share of the mortgage, which is approx £275 per month for the next nine months, then I would want this to be accounted for in my share of the surplus, if that makes sense?
Thanks for all your help so far.