Release and gift deed

If you have only two sons that will automatically transfer to them.

better is to make a registered will deed and after you the property will devolve upon your sons.

No, in my opinion.  The residential apartment is owned jointly by the wife and husband, the husband died, his half portion will be devolved among the wife and two sons.  Hence, her share in the husband's and her 1/2 share may be gifted to her two sons by a registered deed.

If the wife is desirous of giving away her share as well as her share out of her husbands share in the property to her sons, she can first execute a registered settlement deed in favor of her two sons for her half share and can execute a registered release deed relinquishing her rights in the share of her deceased husband in favor of her two sons.

Since the residential apartment was owned jointly by husband and wife so after demise of husband his 50% share in property rights will devolve equally to deceased husband's wife and two sons so wife may relinquish her share in husband's  property toher sons by registered release deed an in regards to her 50% share she can gift it to her sonby registered gift deed.

I concur with the expert advise of Mr. Bhartesh Goyal ji, 50% share of deceased husband / father shall devolve equally i.e., 1/3rd each to widow and both sons. 

She (mother) may gift or execute a will for her share (50 + 17= 67%) in the property in favour of her sons.

Nothing more to add.

It seems that people here  know how to complicate simple things. Most probably the apartmet is now exclusively held in the name of the wife. It is not clear whether the half share of her deceased husband has already been tranferred to herself and her two sons either through book entries of physically. If she is now holding the entire property in her own name and she wants to transmit the entire poperty to her two sons after her demise, ultimately the two sons will be getting the same 50% each of the whole property. It appears now that there is harmony in the family and the two sons have not made any claims. Why do all kind of calculations and create disharmony. Most probably the boys are now minors and not married yet. In due course let them get married and give all those sharing advices to their wives.