Hi
1) The sale deed executed by your cousin is null and void given the fact that there is an execution petition pending on the said property.(it is presumed that you and your cousins were brought on record as Legal Representatives of your father and your uncle in Execution Petition)
2) In order to safeguard and retain ownership within the family, you should ensure to get the property(300 square yards) auctioned by the court by virtue of the said execution proceedings and thereby ensure that the buyer is kept out of the picture and property.
3) The buyer might approach the court for relief on the ground that neither himself nor his predecessor in title( your cousin) were parties to Execution proceedings and hence the auction is not binding on them. So in such an event the court might grant him stay order and thereby stop the auction. So only way to avoid the stay is to ensure that your cousin is also made party to the execution proceedings.
4) Courts will not grant the buyer a stay in the event of your cousin being named as debtor in Execution proceedings.
5) Prior to participating in the auction, you should ensure to get an order from the court that you have complied with your part of 45 Lakhs for and on behalf of your father. You will be eligible to participate in the auction if and only if your name is cleared of your share of liabilities in Execution proceedings.
6) If you are the highest bidder, you should deposit it in the court only.
7) The buyer can also participate in the auction and will get ownership, title and interest if he emerges the highest bidder.
Hope this information is useful.