The grandparents were poor common folk, we don’t expect to find anything of substantial value, but as you say, there’s always the possibility of a “ringer.”
I’d be pleased to be of assistance in doing any research. Once you find out what you have, feel free to FReepmail me details and I’ll get you info. I have a bit of experience in the gun collecting field, but I’m a terrible canoeist.
Be sure to keep the bill of sale for each gun - keep it long after any money or family disputes are settled. It’s unlikely a gun you sell through a dealer will be used in a crime. But if such a thing happens and the police question who owns the guns and they knock on your door, you can prove you don’t own them.