I'm from Bangladesh. My mom is a widow and I'm the only child. While my father was alive, she never worked. She acted as a 'sleeping director' of the company my father used to co-own when she applied for TRV. Well, that's my story.
But I've seen my fellow countrymen getting success for their parents when both parents are alive and any/both of them are employed. I couldn't help comparing my mom's situation. She visited almost 20 countries with my father and never over-stayed anywhere. She was never refused a visa in her life other than Canada. She was called for an interview and told "You're getting profits from your compnay without working, your only son is over in Canada, you can easily sell your properties, leave Bangladesh and live with him permanently" when I invited my mom to attend my convocation. It was me whose study permit was going to expire and they thought we would both live permanently - weird!!!
Seeing your case, your parents have good chance in getting visitor visa since they're both employed and have some properties. But again, you can never be sure about it. You got a negative point as me for not having other siblings (believe me I wished for a bro/sis seeing all these). Your parents visiting your grandmom once a week isn't gonna help much unless they're taking care of her everyday for medical reasons. Research a bit more about your country how they handle cases and how frequent the rejection is.
