Which county does one file probate?

My grandmother died in 2006 and her house has never been probated. She has two living children and six grandchildren. Her will states is would go to her son (my father) who has no interest in paying court costs for the probate. I have paid taxes on the property for the last 5 years. I would to have the estate go through probate. House is in Delaware county, living children in Creek county and North Dakota and I live in Texas. I will find an attorney based on where I need to file the paperwork so I need to know where that would be.