Verbal agreement with my Grandfather, who is now deceased.

The home we live in used to belong to my Grandfather. A couple years ago, he offered to sale it to my husband and I. We attempted to get a loan but weren't able to. So the three of us (husband, grandfather and myself) sat down and made a verbal agreement that we would put money in an account as we were able to. No set amount per month to save was said, nor was a timeframe put on it. If he were to be living when the full amount was there, we would give it to him. If he were deceased, when the full amount was there, it would be divided between his four daughters. None of the daughters were there during the agreement. He then legally signed the house over to us and it is in our name. We have very gradually been putting money aside as we have had some financial difficulties. Well sadly, my Grandfather passed away early December 2007. I have recently been getting emails from 3 of his daughters stating that they want their part of the money now. And one of them has threatened to sue us for her part. Would she have a case in court?