I'm sorry to hear about your dad's passing and that this has been such a frustrating situation for you. If you know the contact information for the lawyer who prepared the will for your dad, I suggest you contact him/her immediately. Exectors should be contacted immediately, and it has been several months. I would send a written request for information about the will and whether or not the heirs have been properly notified.
You can not obtain your grandmother's property unless items of hers were left to you specifically. If they were left to your dad, they would be part of his estate... in which case the will determines what happens to them.
If you believe there may be wrongdoing going on, you can certainly speak to an attorney regarding what legal options or rememdies you may have. You can find one through the locator service on LawInfo's home page at:
http://www.lawinfo.com/. Some do offer free consutlations. Good luck.