I am sorry for your loss. You should seek professional guidance for this scenario.
See https://taxexperts.naea.org/listing/service/estates-gifts-trusts
I have to presume your father passed before your mother and if that is not the case, none of the following applies.
Since you acquired the property from a decedent (your mother), you and your siblings received the property with a stepped-up basis (stepped up to its fair market value on the date of death of your mother).
Accordingly, you each received a one-quarter share (unless you did not disclose other parties). As a result of buying out your three siblings, you have a split basis; one-quarter of your basis is the fair market value on the date of death of your mother while the remaining three-quarters is whatever you paid your siblings for their shares.
