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Is this investment opportunity problematic?
Adding to what others have said, if the mortgage for the new house is backed by the federal government (e.g., through FHA or is to be sold to Fannie Mae/Freddie Mac) you would be violating 18 USC § 1001, which makes making intentionally false statements to any agent or branch of the federal government a crime punishable by up to 5 years' imprisonment. The gift letter you are required to sign will warn you of as much. Don't do it, it's not worth the risk of prison time.