It appears that you have been given only a life interest in the flat and NOT an absolute interest
That means till the time you are living you can live and reside in that flat
So after the demise of your parents your siblings cannot claim any occupancy right in the flat till you are alive
As no absolute bequest is made in respect of the flat, it will devolve by intestate succession to you and your siblings each having 1/3rd share in the flat
So after your parents' death you will have 1/3rd undivided share in the flat and absolute right to live in that flat exclusively for your lifetime
Your siblings would have a vested right of 2/3rd undivided share in the flat and their joint occupancy right would be delayed for the time you are alive
As there is no absolute bequest in your favour, when society goes for redevelopment, the consent/noc has to be given by all the 3 legal heirs
The new rehab flat will be jointly allotted to you and your siblings, however you will have the exclusive right to reside in the new flat for your lifetime. However your siblings 2/3rd undivided share in the new flat will already be there
If your siblings are willing then they can release their respective 1/3rd share in the flat in your favour by registering a release deed
So if you have a registered release deed from your siblings, you will become the absolute owner of the flat and wont require to probate the Will
However the society or the builder may require you to submit a legal heirship certificate or a LA to ensure that your title to the flat is clear