No, you have not been filing so incorrectly as to have to amend anything. Your oversight errors are minimal and considered immaterial. What you should make sure you are doing, for TurboTax fees, is list this as "legal and accounting" fees. In addition, your property taxes can either go on the 1065 and then be adequately allocated to each sibling, or, they can be individually reported on their Schedule A of 1040 - this should be whatever provides the greater tax benefit. Since this is a private property and has never been used as a rental, it is not a business but yes a partnership. You should look into filing it as an LLC for everyone's future benefit. Any other questions, please ask!
