Unless the deed specifies otherwise, each co-owner owns 1/3 of the home. Your father essentially gifted you 1/3 of the home, and that comes along with 1/3 of his cost basis (what he paid). So your basis is 1/3 what he paid, and your taxable capital gain is the difference between 1/3 the selling price and 1/3 the purchase price.
Yes, you have to pay the tax even though you didn't get the cash. You need to discuss that with your sister and father.
