Family and Friend Funding

[Ron West]

I am looking for advice on what are good, normal, or unique agreements when family/friends what to invest in you! 

For example, if I am purchasing a home for $50k and using a 80/20 split with the bank, I would need $10k for my down payment. If my family decide to loaned me $5k or $10k what would be their benefit? I would assume loan pay back (maybe with interest) and a percentage if/when you sell but I would like some clarity. Thank you for your time!