Family Loan options/limitations on Duplex

[Sean Murphy]

Looking for advice/counsel on the financing of a duplex I am looking into. 

The property is listed for $140,000. I've been in the stage of saving up a down payment, so right now I have around $15,000 saved. Lets assume I make an offer for $110,000 and the owner accepts. The required down payment would be $27,500 from my bank to get the mortgage. I would need to come up with the remaining $12,500. 

Which leads me to my question: I have interested family members who have static money that isn't doing much for them in terms of investments, but are there any legal/tax issues, restrictions or limitations that come up from a simple family loan to help purchase a property? I would structure a loan repayment plan with interest with my family internally, but does this raise red flags that I'm not aware of? 

I appreciate everyone's help and time!