The ownership of the house is based on the deed. If his ex-girlfriend is listed as a grantee on the deed along with your father, then she has partial ownership of the property. If she is not on the deed, she is not an owner. Simply being listed on the note does not give her ownership of the property.
You will need to probate your father's handwritten will to transfer legal title to yourself. Contact a probate attorney in your area. I know one I would highly recommend if you need a referral. Just give me a call.
David G. Voeller
Probating handwritten wills is extremely complicated but needs to be done. In my experience the probate court in Williamson County is very careful with these types of cases.
As for ownership of the property you will need to go to the Deed Records office and look to see who is actually on the Deed. The office is located in the basement of the courthouse sub annex in Georgetown. If you are unable to go yourself your attorney can definitely look for you. While there are other ways to look to see who is on the deed online you want to check the actual record to be sure.
I agree with the above. I would only add that her note is not legally binding. It would only be legal if she officially "disclaimed" the property. Then again, if she actually does feel that way, then she might be cooperative if you need her to sign any paperwork to refinance the house; it might not matter, but in these disputes it is best to avoid any conflict, if possible.
I am licensed to practice law in Virginia. Please note that this answer does not constitute legal advice, and should not be relied on, as each situation is fact specific, and it is not possible to evaluate a legal problem without a comprehensive consultation and review of all the facts and court pleadings filed in the case. This answer does not create an attorney-client relationship.
I agree with all above regarding probating the will. Since ex-gf is on the mortgage loan, it is almost certain she is a co-owner of the house, but it is the deed records that tell the fully story. Hire an attorney, probate the will, check the deed records, and consider a claim for reimbursement (takes a long time to explain, but ask your attorney).