The registered gift deed executed by your deceased father in favor of you people which came into effect after the lifetime of your deceased mother is very much valid and your step mother or her children do not have any right or can have any claim for a share out of your father's share in the B schedule property as the same was already transferred by yor deceased father by a registered deed during his lifetime.
Now to the A schedule of property which was in your grandfather's custody till his death. Upon your grandfather's intestate death, the A schedule property shall devolve equally on all his legal heirs namely his sons and daughters. The daughters shall be entitled to a rightful share in that property, provided your grandfather died after the year 1956 wherein the amendment to Hindu Succession act entitling the daughters to an equal share in the father's property came into force.
Now the rights of your step mother and her children;
They are entitled to an equal share out of your deceased father's share in the A schedule of property which shall be originally divided into six equal shares, out of which your deceased father shall be entitled to one such share and the same can be divided among his own legal heirs consisting you, you own siblings, your step mother and her children.