The first thing is you have to prove that you or someone you represent MIGHT be the legal heir. Once you have that proof you start in the local probate court to require probate of the estate. You get the court to appoint an executor and acknowledge the heir.

Yes, the person to inherit will have to have at least some relationship, 3rd cousin, even 10th cousin, something
A person with no relationship can not file a claim. It may be the deceased grandfathers brothers great grand child, but there will be some relationship somewhere