On demise of father your mother , 4 sons , 2 daughters would be legal heirs to property as per Muslim personal law
2) however your sister cannot claim 80 portion of brothers house as her share
3) your brothers should file suit for eviction of sister and her 4 sons
4) seek injunction restraining her from creating third party rights on the property
5) suit for eviction would take years to be disposed of . take the plea that full consideration for land and construction was paid for by the brothers