The fact that they have a child in the UK and can care for themselves also are tough things to overcome. Unfortunately people parent sponsorship is not guaranteed which Canada should do a better job at clarifying for people. Certainly no harm in trying to fight to get approved. For your best chance hiring a lawyer is your best option if you have the funds. If you don’t have the funds to pay for a lawyer I would suggest you also look into the costs associated with parent sponsorship and getting older in Canada. For example if your parent needed to go into a longterm care facility are you aware that you would need to pay a monthly fee for the next 20 years (10 years in Quebec)? Monthly bed fees are usually between 1-1.5k/ month. Given your father has multiple health issues you may be surprised that many things are not covered or only partially covered when it comes to healthcare. The UK has closer to 100% Medicare while Canada is closer to 70%. Things like mobility devices, devices that help people with poor sight,some diabetic supplies are only partially covered or not covered at all. Would suggest looking into this depending on your financial situation and theirs.