Sell 2 houses to buy 1 with elderly parent. What is the best approach for mortgage?

My husband and I are looking to take in his elderly father, who can no longer live alone. We currently dont have the space, so we need to buy a new home. We need to sell his and ours. What is the best approach for a mortgage? Do we get a new mortgage loan with his father or have his father 'gift' us the money he is supplying?

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