Question: - What are option available to me to gain at least the amount paid by me either on LOAN and direct to builder.
You can send a demand notice to your father demanding the loan amount repaid by you in respect of this property and then file a recovery suit based on the evidences you hav for having repaid the loan so far and in the same suit you can seek for Attachment before judgment of the property toweards security for the money due o you from them.
Question: - How can I become the part of the property or joint holder of the property.
You cannot become a joint owner of the property by any means except if they transfer a portion of property on your name by a registered deed/document.
Question: - how can I take the benefit to use this property for leaving.
By acquiring it through legal process on the basis of loan amount settled by you.
Question: Do I need to stop the instalment of bank and lets them fortified the flat and sell then in auction.
You may decide about it after fully understanding the consequences by your such act.