First, the Answer response deserves a failing grade.
Listen to the Commentors. DO NOT BUY THE HOUSE. You are young  and financially in good shape. Do not jeopardize your future where you will be subject to Capital Gains tax if you sell the house. If you don't own a home already but want to buy one in the future, you will be ineligible for 1st Time Home Owner Grants. Not to mention, the added headaches you are going to have negotiating different  provincial laws. You do not want to risk your own credit rating. This is your dad's problem, not yours. Help him to solve it not take it on. Direct him to a Debt Counselling, bankruptcy and credit agency like BDO. They can help him come up with a Consumer Proposal. This will help consolidate debts to a manageable level and set up a budget plan and schedule so that he and your grandmother should be able to pay the mortgage. You could possibly help by paying the property taxes and utilities.  Everyone will feel better executing a financial plan.