Dear sir, there are two issued mixed in this.
Firstly Your father having control over 5 Acres. Does it mean he has purchased the property and he was the absolute owner in possession and enjoyment of the aforesaid 5 Acres.
Secondly, your brother selling some COMMON properties ? How did he do that, was there any GPA ( registered ) given to him to execute sale deed on your fathers behalf ?? Without acquiring any kind right OR title over the property your brother cannot sell it whether it is movable or immovable properties.
Now after Sept 2011 i.e, after death of your father HOW MANY LEGAL HEIRS have inherited the property in question.
YES, ONLY IF IT IS PROVED IN COURT OF LAW THAT your father has taken a loan or he is indebted to some one lawfully, In that case all legal heirs are liable to repay the LOAN / DEBT incurred by your deceased father. Pls note that - NO LEGAL HEIRS have to shell out money from their self earned assets. THEY WILL BE LIABLE to pay ONLY TO THE EXTENT OF INHERITANCE FROM THE DECEASED ESTATE & MOST IMPORTANTLY the court of Law should pass an order to such an extent making the legal heirs liable. The ONUS of burden is purely on the so called SHAM CREDITOR ( as per your narration ) to fight out a successful legal battle for recovering the money lawfully from LEGAL HEIRS.
As per legal notice is concerned I strongly advise you to take professional help from Advocates and send technically strong reply notice immediately to avoid any future complications.
For any further clarification and professional assistance you can write to me on sohan1912@rediffmail.com or cal on 9845285555 in Bangalore.
With Warm Regards,
MAHADEVA RAO G,
ADVOCATE,
BANGALORE.