Who and all coparceners in ancestral undivided property?

A,The residential ancestral property with old building is in my fathers name who is expired in the year 1977 B, My father has 3 sons including me and one daughter who got married in the year 1971 . iam the younger one of all . C,The property is not legally partitioned . but my father divided the building alone to three sons by giving appropriate rooms just orally . my father not told anything orally or in written to give any share in this residential ancestral property to her daughter i.e my sister bcoz my father sold 2 acre of land for my sister's marriage when i was minor that time D,My second brother willing to sell his share to our sister's son. . im ready to buy my second brother share to prevent outsiders to buy . but they are adamant in selling to third person or to our sister's son . my fathers wish is to enjoy the property within our family not to give to others. My questions are #1whether our sister's son will be one of the coparcener? 2, whether our sister's son can buy my second brother share without other coparcener consent / knowledge ?