Your situation is very complicated. More facts are needed.
- Was your grandfather the sole owner of the home prior to adding you to the deed?
- Did you pay anything to your grandfather when he added you to the deed?
- When you grandfather added you to the deed, did he pay any gift tax?
- How did your grandfather acquire the home? If he purchased it, did he purchase it alone, or did he purchase it together with someone else (such as your grandmother)? If he previously owned the home jointly with your grandmother, how did your grandfather become the sole owner? Did they get divorced? Did your grandfather inherit your grandmother's half of the house when she passed?
- SharonD007 is thinking that you lived in the home as your primary home at some point, but you didn't say that. Did you live in the home at any time? If so, from when to when?
There might be additional questions that I haven't thought of. You will need to know the market value of the home on the date that you grandfather passed. (The value when he added you to the deed probably doesn't matter.) Your answers to the questions above will determine what other information you will need.
