I have xerox copies of the actual will. He left everything to Mary Pennell if memory serves. There is also a newspaper article or few to that effect in the Quincy online library archives. That is free and online. Just search on Solomon Hasting or something pertinent like that.
When I looked up other documents and census I believe that she was his granddaughter. Now I'm doubting it because you are so strong in your conviction otherwise, but that's how I remember the will. I don't have a chance to look it up at this moment. I did send copies to some family but got no response, so I didn't bother to upload it here.
They are definitely in Stewart cemetery. I had a researcher go into all of that and someone took photographs of their tombstones. Hope that helps.