1. It depends on how the matter is viewed and/or argued before the Court.
2. If the matter goes to court, your father's/sister's lawyer might claim that you have gifted that amount to your father or has refunded the said amount towards part of the amount which was spent on your education by your father or for on some account.
3. Had you made the payment directly to the builder/seller, there would have been a chance to claim that you had paid 75% of the price for which you can claim 75% share of the said property.
4. Moreover, as per Benami Property (Prevention )Act, 1988, property can not be purchased in some other person's name after the year 1988.
5. So, there is a very good chance of loosing in case you want to file a case claiming 75% share of the said house to be declared in your name as your property.