Can grandson sue grandfather estate

In the United States, anyone can sue anyone. Sometimes the suit has no basis and no lawyer will touch it with a 10 foot pole and it is ruled frivolous and the person bringing the lawsuit loses both his filing fee and his shirt, but, yes, it can be done. Since you use the term estate, you might mean your grandfather just died. You might mean he has a will that is in probate. In that case, you might be better off entering a claim against the estate in probate court. That must be done immediately if not sooner. If you do not understand what is going on, you might see a probate lawyer.