Was the estate closed at the time of the sale? -- I'm just checking to see if the sale was of an estate asset, or if you and your siblings were already considered the owners of the property.

If the estate had closed, or the house had already been "distributed" to you and your sibs, then you would each show one-third of the sale on your personal tax returns on Schedule D. You would use "inherited" as the date acquired, and use one-third of the value of the house on the date your mother died (probably shown on a county probate form) as your basis (cost). Any gain or loss is considered long-term.

The answer depends both on State law and on Federal Law, based upon the value of the entire estate of the person that passed on.