Legal authority

It is believed that you are all Hindu/ covered by Hindu Succession Laws.

The husband (father as in query) is alive?

The property owned by husband (father as in query) is self acquired or ancestral?

Confirm!

If your father married 2nd lady after divorce from 1st lady and 2nd marriage ( in IT’s true sense per valid procedure/rites/customs was performed) then the marriage is valid.

The divorce from 1st marriage was awarded by court of law?

In both cases you have posted there was marriage and probably you mean to mention that marriage as per accepted criteria under law of land/ rites/customs was performed!

Confirm!

The children from valid/void/voidable marriage are legitimate.

In other words there should be performance of marriage.

Child born from arrangement other than marriage may have no right on Hindu Father's property!

If marriage was not performed then you may go thru and pick up the relevant points;

https://www.lawyersclubindia.com/articles/Child-born-from-arrangement-other-than-marriage-has-no-right-on-Hindu-Father-s-property--8467.asp?utm_source=article_mailer&utm_medium=email&utm_campaign=article_followup

Assuming that you are all Hindu,the property is self acquired by father,his 2nd marriage was performed and per test of law is valid or even void/voidable, and he has deceased without leaving avalid WILL ; 

Then;

1. The husband-wife relationship with 1st wife is severed and 1st lady is no more wife hence ClassI legal heir. She may not succeed to have any share.

2. If the kid from 2nd wife is born from a valid/void/voidable wedlock the the kid being ClassI legal heir has a share.

3.2nd wife can dispose her self acquired/absolute estate/wealth/property in her life time by a a valid/registered deed in favor of her son born from her womb. She does not require any consent from anyone in doing so. Her son born from her womb is her ClassI legal heir.

Assuming that you are all Hindu, the property is self acquired by father, his 2nd marriage was performed and per test of law is valid or even void/voidable, and he is alive;

Then

In case of his self acquired estate/property; He can dispose IT in his life time by a valid/registered deed/WILL in anyone’s favor’ be it even a stranger.

He does not require anyone’s consent for IT.

Wife has NO forced share in self acquired estate/property of husband.

Son has NO forced share in self acquired estate/property of husband.

Assuming that you are all Hindu, the property of father is ancestral, his 2nd marriage was performed and per test of law is valid or even void/voidable, and he is alive;

Then

In case of his ancestral estate/property; He can not dispose more than his share in his life time/He can not dispose share of other Co-sharers.

Wife is not Co-parcener in ancestral property of husband. 

Son (fathered from valid/void/voidable marriage), being legal heir has a share in ancestral property of father.

If he has not disposed his share in ancestral property then after his death  his share shall devolves 1st upon his CalssI legal heirs..

If father as in query has deceased then his wife and son from 2nd marriage (valid/void/voidable) being legal heirs have a share.

The property that devolves by inheritance/WILL is of nature self acquired. 

The 2nd wife in that case can dispose her share by WILL to her son (born from her womb) and even her step son or anyone.......... 

It shall be certainly better to show the property/marriage/divorce and birth  related docs to a very able senior LOCAL counsel of unshakable repute and integrity specializing in testamentary/succession/civil matters and well versed with laws/customs related to your faith/community and having successful track record for a considered opinion.

If you have already consulted you may post the opinion of your OWN LOCAL counsel.

First wife of your father, your biological mother, after divorce does not remain his wife and cannot claim any share in his property after his death, if he died intestate.

As far the claim of the son of the second wife who was born to her through her first husband and your father was no the biological father, he is "Uterine blood" or he is your Uterine blood brother. The Schedule provided in the Hindu Succession Act, 1956 in the explanation -- In this Schedule, references to a brother or sister do not include references to a brother or sister by uterine blood. By this explanation being related as Uterine blood his claim in your father's property doesn’t exists as he has claim in his biological father's property.

​Yes the second wife can leave Will in favour of her biological son to be beneficiary of her share in the property that she gets from your father.

I missed out few points - My father is not Alive and the property is not ancestral.

But I got the answer from MR  Vijay Raj Mahajan and Kumar Doab  in the forum - Thank you all
 

The 2nd lady's child from her previous marriage is not bilogical son of your father (her 2nd husband)....................

and probably  he was not duly adopted per valid adoption procedure/deed.

Refer to the points pertaining to father being not alive and property being self acquired.

You are welcome!