Property dispute

All legal heir of your father are entitled to get equal share in property  so your sister's daughters can claim their mother's i/4 share in property. 

Sir they are claiming 50% share in the property

As per Hindu law of succession, since your father's first wife died and subsequently he married your mother, your mother becomes his legally wedded wife.

Now, as per law the legal heirs to succeed to your father's estates shall be his daughter from first marriage and the second wife and her children.  All are entitled to an equal share in the properties left behind by your deceased father.

your step sister has no rights to claim half share in the properties, you can refuse, let she go to court, the court will not entertain her claim because it is against the provisions of law.

If it is the father's property, the step sister (or her legal heirs) is entitled only the one fourth share. 

Had the father inherited any property from the deceased first wife?

No Sir, This is my father's self acquired property . And our half sister has also expired, now when we wanted to the tranfer the ownership to our MOm, expired sisters three daughter are asking for 50% of propoerty to gibe there consent

Your deceased sister's daughters have a right over the share of your sister only, and they are not entitled to a 50% share.  Let them go to court, it goes as per the law.

They are claiming that they have high share as shares of their mother and granmother adds to them being daugter of dad's first wife 

Let them claim even the entire property, you can challenge them legally as per documentary evidences and merits.

Sir by any chance or any section their claim is relevant, as I need to very cousious. Further they are not giving their consent when I am transferring the flat on my Mom's name, the only delay happended from 2020 to till date beacuse the propeorty was mortgagaed for 31 lakhs loan. Even Nomeene is Mom in society papers

Don't post questions of imaginary concept, you can challenge their claim when they make one.

You have been advised of the steps to be taken in any such event hence you may follow it or confide in your adocate on all such future incidents.

The tpne and tenor the above posting places the query in a different perspective. The children of the step-sister are under no obligation to act at your behest. So also, a nominee is only a trustee on behalf of the legal heirs. 

Who has mortgaged the property?

Hi sir,

Dad has taken 31 lakh rupees loan on property. Which was paid by me and my brother.