Power of Attorney Given By Minors

Question: A person died leaving behind 3 kids and wife. according to his will all the Kids were to inherit their shares automatically attaining major age status as per Indian Laws. in the meantime all the kids made the mother to manage their assets through registered Power of Attorney without powers to make any sales or transfers in the period of their being minor. now the question the mother used the assets to maintain the expenses of up bringing of the kids and further on but till her death did not hand over the assets of the hiers according to their share as per original will. Now after years of staying with the youngest kid she has jointly made fixed deposits with this youngest in joint name. and the youngest son is not giving other son's share saying that the entire expenditure done till date by mother has come into your share and hence no share. Can the Mother give all the assets of her husband to the youngest son and is the power of attorney of no relevance now.