Can a will disinherit stepson and ex-wife ?

He is not a step son.

So long as the property is the personal property of your father, he has every right to dispose of the property in whichever way that he likes.  He can therefore WILL the property to any one he wishes (in this case your mom and you). 

However, since the property would be WILLed, the same can be challenged by anybody (including his first wife and son through her) on any ground that they find suits their case - but it is for you, the beneficiaries, to establish and defend that the WILL.

How will the probate process work ? Will we have to notify the first wife and her son when getting the probate ? We have no knowledge of the wherabouts of the first wife and son .

Need Advice,

Just check your fathers divorce decree. If there is the clause that the ex-wife or his son cannot claim anything in future and the alimony is for all the claims in past, present and future, then your fathers ex-wife or his son cannot demand anything from your fathers will. Secondly, if your father has made the will and gave the reasons why he is excluding the ex-wife and son, then this would be difficult to challenge.

Can somebody please describe the probate procedure ? Do all living heirs have to be notified ? Will we have to go to the High Court to do this ?

The question of probate of WILL, would arise only after the death of your father. Currently, I believe your father is still alive.  Therefore why are you now itself bothered about the probate process.

Further whether probate of WILL is required or not is also dependent upon where the property is situate.  Probate is not required at all places - though it is required in Chennai, Kolkatta, Mumbai, Delhi and other notified places.

Can POA be a substitute for a will ? Can POA be in effect when my father dies ?

If the POA is given by your father, then it will lose its validity immediatley on the death of your father.  Thereafter it will have no value / effect.

he (the boy) is step brother of you and step son to your mother. he is real son to your father.

it is sure that divorced wife will not get anything, but your step brother may claim. it is his right.

for will, information to any of the benificieries not necessary.

arup - are you saying for probate process all beneficaries do not need to be notified