The thug then gets to his feet and runs off - leaving the till behind.
Dolly and Gulamai were shaken but not seriously injured, with Dolly only suffering a cut to her hand.
Cops are now probing the incident, which took place at 8.30pm on Sunday.
The couple's daughter-in-law, Ash Karim, 35, said: "This man came up to the counter and he pointed the screwdriver at her and demanded the money from the till.
"She turned around and went to grab this little stick in self defence.
"Then he literally grabbed the till from the counter and picked it up.
"She is hitting him at the same time and he started to walk off.
"My father-in-law was sitting in a chair towards the back of the shop and he heard her screaming and saw the guy.
"He jumped on him from the back and tackled him down to the ground. The man then dropped the weapon and ran straight out of the shop.
"My mother and father in law are in their seventies but they are quite fit and healthy. My mother-in-law is quite shaken but we just want to raise awareness about it.
"Nothing like this has happened before. I think my father-in-law is so brave for doing it.
"It's quite worrying at the same time. The guy landed on top of him and there's a little step there - he couldn't smacked his head against it.
"He is a hero for doing what he did, but as a family it could've gone the other way.
"It all happened so quickly - luckily he didn't hurt himself.
"I hope we can catch the people who did it."
Police officers are investigating the raid.
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