My cousin has been paying property taxes for over 30 years on his fathers property. He is now 83 years old himself.

I'm going to move your post to the real estate area as you are more likely to get a response there (this is also a probate type question).

The worst myth in real estate is that if you pay the taxes you can own the property. Your cousin needs a lawyer who can handle a partition suit because that is what it will take to sell the property. And it is going to be expensive under the facts you provided.

I do not practice in your state. However, this is common here in FL. Probate must be opened for the estate of the rightful owner - sounds like the father. That will determine who the property descended to upon death of the father. It may be according to a Last Will (is there one around? or recorded?) or it may be according to the laws of intestacy. Here without a Last Will the children inherit the home in equal shares. Have your cousin see an attorney immediately to discuss this issue. Have him bring all documentation to the meeting. Good luck!