Is probate of will mandatory in kolkata. It's cost

Mrs Amita was sole owner of two story bulding in kolkata which she had bequeathed in favour of her eldest son's ( deceased) wife( 2nd floor) and in favour of younger son (1st floor). Younger son has been named as executor. She also executed gift deed donating 2nd floor to eldest son'so wife (as mentioned in the will) and registered the same in the office of sub registerar. AMITA expired on May 2012. Now, my question is how her younger son transfer his portion ( I.e. 1stfloor) in his name.. Some one advised that younger son being executor needs to probate the will and then he should go to sub registrars office under jurisdiction to register the transfer. This procedure seems to be costly as executor, younger son has to pay court fee, legal fee for probate and also legal fee and stamp duty for registering the transfer of 1st floor of property in his name. It will of great help to get an expert opinion. Is there any maximum limit for court fee in case of probate in kolkata.