If they sell it to you subject to the existing loan balance, then it could be viewed as them gifting you $20K. 

Might be best for me to just help my family member by gifting them money for a down payment on a single family home and working a separate investment deal.

You can ask the seller to include it in the sale, or you can talk to your real estate agent about buying it as a closing gift.

All contracts, options, or other devices not based upon a substantial consideration, or that are otherwise employed to permit an unlicensed person to sell, lease, or let real estate, the beneficial title to which has not, in good faith, passed to such party for a substantial consideration, are hereby declared void and ineffective in all cases, suits, or proceedings had or taken under this chapter; however, this section shall not apply to irrevocable gifts, to unconditional contracts to purchase, or to options based upon a substantial consideration actually paid and not subject to any agreements to return or right of return reserved.There is a case going on at this time filed in Collier County.

Brennen, if you receive the house as a gift, you are going to get hit for income taxes on the gift, you should talk with a accountant and or lawyer as to how to transfer this with minimum impact. also, depending if your grandfather has been treating this as rental income and depreciation, he may also have tax implications on a gift transfer.

Bonus could be standard commission bonus, or offered as a gift card of their choice (so then they dont have to split the bonus with their brokerage).

He's quite gifted in creative finance.

My son just graduated from college and as a graduation gift, my husband and I told him that we would buy a rental property and make him a partner in that deal, so now we have to finally take some action!

Most likely these are departing "gifts".Since we have owned the building for two years, the natural question is "why didn't we take action sooner?"  

They will also allow gift letters, where some of the down payment can come from a relative.