Probate of Will vs Mutual settlement

We are 2 brothers,Both married with a sibling each. My elder brother residing in Kolkata and me residing in Gujarat due to my job and have intentions of settling in Kolkata after my retirement. My mother is still alive and my father passed away 4 yrs back leaving a registered will in favor of us which states that my mother will be owner of both the houses in Kolkata till the time she is alive and thereafter one of the houses will be vested to my elder brother and the other to me. The house where my mother currently resides is a stand alone house & is supposed to get vested to me in future in her absence, and the roof this same house was gifted to me by my Father before his death through a registered deed. The house where my elder brother is residing is the house which as per my father's will get vested to him in absence of my mother. It is a portion of the ancestral property(through partition deed) and consists of 4 rooms (2 on each floor) but 2 rooms of this portion is still occupied by an old tenant and brother is occupying the rest 2 rooms available on the floor above. Both of us have no issue between us and agree to occupy the properties as mentioned in the will, except the fact that my elder brother feels somehow the portion enjoyed by him and will get vested to him in future (after mother's death) is lower in value and facilities compared to what the stand alone house that will get vested to me in future, and i do agree to some extent, hence will like to go into a mutual agreement on a registered paper to compensate him for once and forever and tantamounting to an NOC to the stand alone house We are yet to probate the will. My questions are as below. 1. In the current scenario who are the owners of these properties? 2. Once probate done who becomes the owner of the property and does the same add any value to the current postion? 3. Does probate makes the Gift deed of roof of the stand alone house null and that case is probate a good solution ( i incurred expenses to register the gift deed) 4. Is a mutual settlement between us through a registered deed wherein I compensate my elder brother in lieu of the disparity in the property as per will ....and keep this document as a settlement forever and hence do not do a probate at all. 5. Will the above settlement (as per above point 4) stand good even after my mothers demise? 6. Please do provide any additional suggestions as you learned men deem fit.