Your parents have a pretty good chance of approval. For the best chance of approval ask for a 2-3 week visit. They can apply on the same application. You can specify that as a married couple they share their assets even if only one name specified in the account or deed. I would present their account as savings and I would not go into detail about income from their convenience store going into the account or you and your sister financially supporting them. I would provide evidence of the fact that they own a convenience store. A rental agreement, tax registration, etc. I would specify their plans for running the store while they are away or whether they will close during their visit so need to return to open up the business. Would specify if they both work there, if they are the only employees, etc. If your parents need to be in the country every year to receive a pension I would specify that. Proof of property ownership like a home and if possible evaluation of the worth of the property or a general estimate. Would specify that this their retirement property and that they had been living and working in the UAE. Would include proof that they had lived in the UAE and Hadley returned home to retire. Do they help care for anyone like grandchildren, their parents if they are alive, etc.? In general you want to show that they have their own funds to pay for their trip even if you will be paying for some of it or they will be staying with you for free. There are cases where there has been family breakdown while in Canada and then people are stuck in Canada without any savings so IRCC usually wants to see that visitors have the funds if they ever need to pay for a hotel, a plane ticket, a small emergency, etc. You also want to show why they won’t remain in Canada like what they own, their commitments in their home country, if they have residency requirements to receive government funds, etc. Do not book a plane ticket in advance. If you are trying to secure a decent priced flight make sure the flight is 100% refundable.
I would also specify that you had an online convocation already but the school is having an in person convocation and so you wanted your parents there to enjoy the special occasion that they worked hard to help fund. Would highlight that you haven’t been able to spend time together for a long period of time. Would also indicate that you want your parents to see where you are establishing your life as an PR and hopefully a future Canadian citizen and where you went to school do they can picture your life in Canada when you talk to them while they are in their home country.
Gave you some ideas of a few ways to sell the visit but would try to keep the information short and sweet and as well organized as possible and limit the filler so that a visa officer can read through the information relatively quickly and get an idea that they have lots of reasons why they will return home after your visit and are genuine visitors.