A good phrasing for LW would be, "Yes, we are very grateful! Granddad's $15,000 gift on top of the profit I realized from the sale of my condo enabled us to qualify for a mortgage." Be very specific about how much from granddad, because that is the number everyone gossiping about this really cares about. Be as specific as desired about the condo sale proceeds. Shining light on this kind of thing really does help cut down backbiting, and it sounds like there's some of that going on.