Police said the robbers waylaid Ganesh Shet, owner of Mahalasa jewellers at Uppunda, his son Sudheendra Shet and daughter Divyashree while they were returning home after closing the shop.
When Sudheendra retaliated, the gang attacked them with knives and other weapons and fled away with the gold and cash grabbed from them.
Shet, his son and daughter were admitted to hospital with serious injuries.
Three members of the gang were taken into custody, while one of them managed to escape. Byndoor police had registered a case and investigations were on, police said.