I'm not sure if this is the same Sir John Molineux, but there is a man by the same name, and the same coat of arms who is the 4th son of Sir William Molineux of Sefton by his first wife Joan Ellall. Sir John returned to the Great Council at Westminster 17EdII, which is 1323, so he is at least a contemporary. My sources are Memoir of the Molineux Family by Gisbourne Molineux, F.R.C.I., 1832 and The English Barontage... Vol. I, London, 1741. These sources do not mention Margaret, but three other daughters: Agnes, who married David Blundell, a nameless daughter who married Robert Erneys, and another nameles daughter who married Charnock of Aston. Each generation of this family is traced back to the Norman Conquest in these sources.