Sister Sledge

Sister Sledge is an American musical group from Philadelphia, Pennsylvania, formed in 1971 and consisting of four sisters: Kim Sledge (born August 21, 1957), Debbie Sledge (born July 9, 1954), Joni Sledge (born September 13, 1956), and Kathy Sledge (born January 6, 1959). They are granddaughters of the former opera singer Viola Williams. The sisters used to perform under the name of "Mrs. Williams' Grandchildren". The group is best known for their hit songs "We Are Family" and "Frankie".

source: Wikipedia