1) Since your father had made a new WILL wherein he has stated that law of inheritance will prevail for his house property, the earlier WILL will stand revoked vide Section 70 of Indian succession Act (the governing act for Wills).
2) So, technically the earlier WILL executed by your father will be construed as revoked and has no legal validity with effect from the date on which the new WILL is made by your father.
3) No, your father has not died intestate. Since he executed a New Will wherein he has mentioned that the property will be inherited in accordance to law of inheritance, his class I heirs ( 3 sisters, 1 brother ) will inherit the property in equal shares.
4) All surviving legal heirs ( 3 Sisters and 1 Brother) will inherit the house property in equal shares and if the building is divisible by meets and bounds (i.e physical partition of property is possible), then each one of you can also do physical division of the house property.
5) Where physical division is not possible, interested legal heirs can buy out the share of other legal heirs based on fair market valuation obtained from independent government approved valuer's.
6) At Delhi, an application for probate of Will has to be made before the court and court will examine one of the witnesses and then validate the WILL.
7) In general, if all the legal heirs agree that the WILL is genuine, actually there is no need for probate of WILL of through courts.
8) However probate of WILL will stand in good stead when the house property is inherited by the children of present legal heirs.
9) In cases of no contest WILLS, courts will fast track the procedure and you can get a judgment and decree within 6 months.
10) If any of the legal heir is living outside of India, then, they can grant special power of attorney to the other legal heirs living in India to complete the process.
Hope this Information is useful