1) your family is liable for father debts only to extent of property inherited by the family members on father demise
2) you have not mentioned what is the value of father share in flat and the value of the flat as on date
3) if the loan amount is substantial better option is to let bank auction the flat for repayment of its dues .
4) in case fiancier files any case to rrecover the loan amount deny your liability to pay
5) atke the plea that you inheirted only liabilities and no assets on father demise