Hi,
Your parents must prove they will return to the UAE. You can write a Covering Letter for each refusal reason. Evidence for this is important.
Family Ties evidence:
Your parents and you/your brother live together in the UAE + your parents are dependent on you/your brother
Financial:
2-3 years ITRs for your parents + 6 months bank statements (any large deposits must be explained with proofs)
List all financial investments, pension, income from sources, etc owned by your parents. Also, their credit cards (with credit limits) + 2-3 months credit card statements if the dues are low. Prepare a table + evidence.
You can submit a letter of financial support (an affidavit that says you will pay for their airfare and expenses for the visit).
You can either transfer an X amount of money to their bank account or buy Forex cards in their name topped up with CAD for their visit.
Do NOT forget to submit an explanation that you have purchased the Forex cards/you have transferred the money to their bank account.... also submit your/their bank statements to prove this (highlight these Forex purchases/bank transfers).
Prepare a day-by-day itinerary listing tourist places, activities, etc when they visit Canada + expense estimates..... and prove they have their own finances to cover this visit without depending on your paternal aunt. Keep the visit to 2-3 weeks.
Invitation letter from your paternal aunt stating she will provide accommodation + take care of their travel/living expenses.
Other Ties:
Property in their home country: Property ownership documents (translated into English by a certified translator) + assessment by a CA for current market valuation + property tax receipts + if they earn a rental income then proofs of this
Dubai Flat: Lease agreement copy + proofs of rent payments + proofs of bank transfers for this
Travel: In the Covering Letter, you can give the visa details + entry/exit dates/purpose of visit for their UK visit + scan their UK visa and submit as evidence
Other points:
Can they show a *must return to the UAE date* with evidence..... such as a family event?
Overseas travel medical insurance policy: It's not mandatory but a good idea to buy this refundable policy for the exact dates of their visit + submit a copy with the TRV application.... and state this in the Covering Letter
Refundable round trip flight tickets: Again, it is not mandatory but it shows they have every intention to leave Canada. Do keep in mind TRV processing time for the flight dates
Any other responsibilities/commitments in the UAE/home country? List these with evidence
Cheers