I am so sorry to say that if dad did not leave a will, his wife probably has priority over kids as regard disposition of the ashes. But if no will, and if dad had any separate property, you would be entitled to 1/2 of the separate property if you have no siblings. Separate property would be any property your dad had before his marriage, and that he did not commingle. This is a general response and other pieces of property might or might not be separate. You need to consult with an attorney...
You can go to the recorder's website and check title on the property. If the aunt held the property in joint tenancy with her dad, then she could have transferred title to her following his death by submitting an Affidavit of Death of Joint Tenant. Otherwise, she could not have transferred title. If your husband's mom is the named executor, she should meet with an attorney familiar with probate.
It is irresponsible to answer these questions without a complete review of the estate, the will, the assets, etc. The other attorneys are absolutely correct. If you do not have a probate attorney, you should consult with one immediately. You have a fiduciary duty to the beneficiaries/heirs of the estate.
Options are that you reach out to him and ask him to sign a Consent for step-dad to adopt. Tell him this is what daughter wants, or file a Petition to Terminate his Parental Rights, or wait until she is 18 and step-dad can do an adult adoption without bio dad's consent or notice.
There is more to consider. Is the car your only concern? Did he pay cash or is their a loan? If a loan, the car depreciated when it rolled off the lot and may well have no value. Did you otherwise get a good deal? Talk to an attorney who practices family law for guidance.
If an estate is under $100K, a probate is not necessary. But the law does require the Will be filed within 30 days of knowledge of death. A Petition to Set Aside pursuant to the terms of the will can be filed.
If a will is not found, property passes intestate. Nevada has a statute that sets forth the succession without a will. Someone does have to file a petition with the court to appoint an administrator if there is no will. Titled property cannot pass without a court order.
I agree with my colleagues as to your options. I just want to add that probate occurs in the county where the deceased resided. Since Arizona law applies, you should meet or speak with an Arizona probate attorney to determine the best course. A letter from that attorney to the girlfriend might be the way to go.