That’s tough. The only way I was able to part with my first harp was to trade it in as a down payment on a larger pedal harp. The young woman that bought my first harp was to play it in her church in San Antonio TX, that gave me a sence that it was going to a good place and would be well cared for. I did get teary eyed as she and her husband drove off with it ( I even stopped them to give her a few gut strings in case one or more broke in the tranport!). Because of that sale I now have a concert grand that I play at my church, it’s my baby now and I know that my first harp is happy in that church in San Antonio!
If you don’t really need to sell it, and don’t really want to let it go completely because of the connection to your grandfather, perhaps you could either rent it out, or lend it to someone who really can’t afford to buy or rent.