Invalid will in SC?

My father passed away, leaving a will, signed but witnessed by a heir.

Of the potential heirs, one was written out of the will due to many years of legal problems and substance abuse. This heir is not happy about it, and sees nothing to lose by challenging it, and thinks they can do it representing themself.

What kind of leeway does a probate judge have in such a situation? Can he look at the invalid will as a testament to the deceased intentions, using the testimony and evidence of past legal and drug problems as reasoning to divide the estate as written in the will?

Are the judge's hands tied by the law to include this "problem heir" in the division of the estate?