He owned the property with his girlfriend he died before the transaction was done his girlfriend said after his dead that she will honor his wish now that the paperwork is ready for her signature she is refusing to sign do I have the legal right to his share of the property?
The fact that she says she will honor it and then changed her mind seems to indicate the property was as tenants in common or she would tell you she owned it all now as a surviving joint tenant. That being said, you should open a probate and ask to be appointed Administrator to get what is yours. There will be an intestate probate so it will go to his heirs and his surviving spouse and his children will inherit his share. California does not recognize any common law marriage. If she won't work with you on this, you really have no option but to find an attorney.
Use the AVVO.com web site to find an attorney in your area. In addition to that, contact your local bar association for referral to an attorney who specializes in this or talk to friends and neighbors to ask about an attorney they have used and liked. Often, but not always, the attorney will do an initial consultation free of charge. You will then be in a better position to determine what to do next. Best of luck to you!
Your question does not indicate how title to the house was/is held (joint tenancy, tenants in common, living trust), which will dictate how you will need to proceed.
The property may need to go through probate.
Generally speaking, if no probate is needed and if the girlfriend is now the 100% legal owner, you would have to file a lawsuit to "quiet title". However, this is a long and expensive process for most people. And the chances of winning will depend upon what evidence you have to support your case.
You provide very few facts, but it sounds as though you cannot force his girlfriend to transfer a portion of the property to you. You don't indicate how the property was held, but if it was held as a joint tenancy with right of survivorship, his interested would have vested in her at the time of his death. If, instead, it was held as tenants in common, and if he died without a will, then you may be entitled to an intestate share of his property.
You may wish to consult with a local attorney, and to provide additional facts, as well as a copy of the deed to the property.
Good luck to you.