“To and in favour of the said Thomas Thomson, my son, in life-rent for his liferent use allenarly , and to his heirs whomsoever, to be lawfully procreated of his body; whom failing him and his heirs, viz. the said Thomas Thomson's heirs, arriving at majority or marriage, to the said Katherine and Elizabeth Thomson, my daughters, in life-rent, for their life-rent use only , and to their children procreated, or to be procreated, equally among them in fee , heritably