Indianajo has some good information for you there.
This is one of those situations, in my view, where the intrinsic value of an object -- in this case, your nan's piano -- is much greater than the market value. It is also -- since it is an antique -- one of those situations where it is almost impossible to put a monetary value on the object.
You might get lucky and find someone who wants it, either as a piano or as an antique object, and is willing to pay good money for it. Frankly, it is more likely that you won't. Looking on eBay just now, I find several Bechstein grands (no uprights) with good prices on them -- and no bids. Ditto Steinway uprights (one has a bid of $385.00, the others no bids). If you are in North America, you might get $500 for it. You might have to pay someone to take it away. You might, as I say, get lucky...
In my view, I would keep it -- and even have it brought up to tune, if you liked -- rather than try to sell. That is, if you can. Can your husband spring for five tanks of gas? Or 3 weeks extra groceries? For something which is a valued family treasure?
I hope you can go that route.