sorry for your loss. we don't know what your father did. we can't see the relevant documents. if he removed himself completely from the title (no retained life interest) then he made a gift to you and your siblings of the total ownership of the property. in such a case his basis transfers to the donees pro-rata. on the other hand, if he retained a life estate that would mean the donees would use a prorata portion of the Fair Market Value on the date of death. check the title (deed) documents which hopefully were registered with whatever local government agency deals with them. this varies from state to state.
why do you trust this public forum, on which anyone can post any answer more than an attorney in your father's state? they can't answer because they likely did nothing to check the deed and any other relevant document.
there should be no reason why an attorney in your father's state can't give you a definitive answer once they review the relevant documents.
i would say get this resolved ASAP or you may find your siblings filing a lawsuit against you with the possibility that all the legal fees will come out of your pocket not theirs.
