ooohhh, i get it, it said two grandmothers and granddaughters. So the grandmothers must have had sons and not daughters, but where the sons get woman to marry to??
the grandmothers had sons, the sons(2 husbands, 2 fathers) married the different grandmothers (2 wives, 2 mothers) producing grandchildren (2 granddaughters, 2 daughters) for each party and the 2 daughters and the 2 maidens