Well the subject looks to be Ruth gleaning in the field (story from the Bible). If you do a search for the two words 'Ruth' and 'gleaning' in Google Images you will bring up quite a few paintings that are similar; although not, unfortunately, the one you've pictured in your post. Which is understandable as the original painting has been in their family for so long. There doesn't appear to be a signature on the painting either, at least not one I can see from the photo. So a bit of a mystery. Your best bet, as others have mentioned, is probably some kind of fine art valuer.

Regards

Su