You need to make it simple. Explain to your grandfather how it works the First Look Initiative Program. The on-going initiative offers owner occupant homebuyers the ability to purchase HomeSteps (Fannie Mae) homes, during their initial 15 days of listing, without competition from investors. The purchaser does not need to be a first time homebuyer to be eligible provided, however, that they are buying the home as their residence."
So, if your grandfather wants to help you he should deposit the money in your account and all problems are solved. Keep in mind that this does not mean that Fannie will take any low offer during this time. To increase your chances, come with a full price offer. If it looks like a very good deal, go over asking. Wish you the very best!