Balakrishna Moorthy (63) running a book stall in Chinnampalayam had taken Rs 95 lakh loan them to expand his business. However, he failed to return the amount, following which they reportedly started harassing him.
Dejected over this, Murthy, his wife Usharani (53), son Balavijayaprajash and his wife Nithya (30) reportedly consumed poison, leading to the death of the son and wife.
Murthy and Nithya were undergoing treatment in hospitals, they said.
The trio were produced before a judicial court in Pollachi and remanded to custody.
Police said a hunt was on to nab another person, who was absconding.