Your parents must meet the CRA qualifications to claim the eligible expenses as "Attendant Care" under Medical Expenses. Eligibility includes having an approved T2201 Disability Tax Credit form filed with CRA and having a detailed statement from the establishment showing the amount paid for staff salaries that apply to attendant care services. Rent paid to a retirement home is not an eligible expense and the home must provide some sort of care.
From CRA: You can claim the fees for salaries and wages paid for attendant care services or care or supervision in the following facilities:
Please read the section in the following CRA document titled "Attendant care & care in a facility".
https://turbotax.intuit.ca/tips/tax-tip-can-i-claim-nursing-home-expenses-as-a-medical-expense-5239