I would advise that you ask a few mortgage companies about this plan.
Based on limited knowledge of the housing market, you are planning to do 100K worth of work to a house worth approx 300K, which will, in my limited laymans opinion not increase the value of the house at all, in the current market.
The mortgage company will have to agree to the plan, and will tell you if you will have to have the house in your name to get the mortgage.
If they do this, you will be liaible for Capital acquisitions Tax (CAT), but I think that 300K is below the threshold for a gift from parent to child.
If they do give you the house, your parents also need separate legal advice as you will have to draw up a contract giving them a legal right to live in the house, for the rest of their lives and they need to seriously consider the life long consequenses of giving away their home.