Wife’s share in estate left by husband

Dear PAO,

My mother (widow), who is living now with her common-law-husband, is claiming she owns half of the estate left by our father (deceased) and she will also have a share in the remaining half. My siblings and I have no knowledge as to our shares so we would like to ask if the remaining half of the estate will be divided among the children and if my mother will still share in the said portion.