Purchasing a house with an elderly parent. What legal precautions do I need to take?

Purchasing a house with an elderly parent. What legal precautions do I need to take?
Added (1). He will be providing the down payment and we will be financing the mortgage together. I am concerned that this will effect his ability to be covered by medicaid and if something should happen, medicaid could take my house away. I have small kids and don't want any financial ramifications from my dad's health bills. He is healthy now (76). But I am looking into what the future.

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