My father who I have not seen in 26 years. I am 56 my dad was 77 I just spoke to him this Xmas he called me to clear the air and reconect.
I have a living brother and a sister. My dad also has a living brother and sister ( my aunt and uncle)
My dad had been taliking to his sister and to my brother via phone for the past 5 years or so.

My dad met his girlfriend (Katie) 30 years ago she is my age now 56 we think they got married not sure.

Anyway we just found out June 24th my dad died of heart failure of some sort, but he died on May 10th. Katie waited 45 to tell us.
Katie called my uncle and my aunt and said he was dead and buried in Ohio.

My dad and katie had just moved from Fla. To Ga. In the past few months that is where my aunt and uncle live.
Anyway katie called 2 days ago and told them my dad had died but not tell us where he is buried.
My sister works for a County Clerk of Court in NC and my brother used to be a bail bondsman so they both investigated for a few days and found out my Dad was cremated not buried in Ohio like katie said.
Also we found out that when Katie was asked the question on legal forms if my dad had any living relatives she wrote down NO.
We are sure she has broken several laws and trying to see what our next moves are What can you share with me.

You can find out more that is on the record, but you will get nowhere with her lying. You won't be able to prove that she knew about any of you, and even if you could, what would your damages be?
The steps you take are to find out if there was a will (from the probate court where he died) and if they were married. Finding out if they were married or not isn't going to be easy, but can be done. Start with the state of GA records. The probate court (if used) might have that information.
Blaming her for waiting 45 days is a little unfair, don't you think, if NONE of you were even trying to contact him during that time? She had her hands full with hospitals and laws regarding death. If he had no money, her problems were many. If he did have money but no will, she had problems.
I'm sorry you didn't take the call at Christmas as a sign that he knew he might be dying, and go see him, and spend some time with him. I see no reason to add bitterness about the woman who stood by him for 30 years.

Plus, saying he was buried when he was cremated isn't contradictory necessarily. Many people bury ashes. And how do you know she didn't take them to Ohio?

What is really going on here? You and your siblings and aunt and uncle can have a service.

I'm curious, what do you hope to gain from proving he has living relatives? You were estranged from your father. Do you know if he had a will? You don't even know if he was married to this women. Do you just want to be validated as a living relative, or is there more to this?

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I'm sorry you didn't take the call at Christmas as a sign that he knew he might be dying, ....

Not that it really matters, but I believe you misread something:

"... I just spoke to him this Xmas ..."

I meant 'I'm sorry you didn't perceive the call as a sign.' I said that because that seems to be the one and only contact he has had with his father in the last 26 years.

"Katie waited 45 to tell us."

45 days, months, years?

What should you do? Nothing. That window closed 26 years ago. Now he's dead and you want part of his estate - after 26 years of no contact?

To be fair to the OP - if the father died intestate in GA then his estate passes 1/2 to the spouse and 1/2 to the children (the OP in this case). But if there are no children then it all goes to the spouse. So it could be that Kate is trying to grab the entire estate for herself, illegally, by claiming that there are no children.

To the OP - you need to go to the probate court where your father was living in GA to find out whether there was a will and who has been appointed as personal representative (executor). Then contact him/her and demand an accounting of the estate.

The OP doesn't know if father and Katie were married, yet she filled out some type of forms.

There's lots to be discovered - including whether father was actually resident of Ohio or Georgia. If father moved to be closer to family, family presumably knows!