mother share in partition

If father died intestate then his self acquired property rights will devolve to his legal heirs equally 1/3 to each mother and two sons.

In case A (Father) has executed a will then as per will (Under Indian Succession Act, 1925 via Section 30 of Hindu Succession Act, 1956).

But if A (Father) has not made any testamentary disposition i.e. died intestate then [B (Mother) and (Children) C, D]  all three are Class 1 legal heirs which shall take simultaneously 1/3 share each. (Under Section 8,9,10 of Hindu Succession Act, 1956).

If it is ancestral property mother gets only 13 guntas ,self acquired died intestate all  gets equal share if they are Hindu's ,others as per their personal  family law or as in Indian succession act .

Yes.  agreed with above experts.

1/3 to each B,C and D , if there is no will.