We have a house that has multiple owners on the deed. I want to buy them out. I have been living in the house for 13-14 years doing all the repairs

You should probably start with the current fair market value of the property, and then discount that value by the dollars you have been spending on taxes and repairs.  There is going to be some give and take because while you have been doing the repairs and paying taxes, you did not indicate whether or not you have been paying the other owners any rent. It could be that the costs you have incurred would be off set by any rental charge they could have gotten for the property.