Probably not very much.
If the house was inherited (and not passed by gift or something else) then the cost basis is the fair market value on the date of his death. Any capital gain would be the difference between the selling price and the cost basis, so if the home was sold fairly close in time to the date of death, then the cost basis and selling price will be about the same and there will be no taxable capital gain, even though the cash proceeds might be significant.
If the home changed value significantly between the date of death and date of sale (a rapidly changing real estate market) then you might have a taxable capital gain, or even a deductible capital loss, if housing prices dropped. You would want a qualified appraisal to document this. If there is a taxable gain or deductible loss, then each sibling would report an equal share (half, thirds, quarters, etc.). You may want some professional help if you think there is a significant gain or loss.
If the house was transferred by gift or in some way other than inheritance, you should get legal/tax advice from a professional.
If there is a taxable gain, expect to pay 15% federal capital gains tax, or 20% if your total taxable income is more than $250,000 (single) or $400,000 (married). Most states tax capital gains the same as regular income, so between 3%-13% depending on your state and your other income.
