The answer to your last question depends upon whether your mother died in Pennsylvania. Her estate would be probated wherever she was domiciled at the time of her death.
All the other questions are answered by this: the will is invalid. Unless there are other facts here (such as a subsequent (and properly witnessed) amendment which re-published the will), then the will is a nullity. A beneficiary's witnessing a will essentially negates the witness signature. There's really nothing for a judge to decide.
Consider hiring a lawyer. This kind of stuff gets dicey.
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I would take the Will to an attorney for purposes of having it declared valid or not by the Judge. Once you have a determiniation from the Judge you can make further decisions regarding the distributions. Generally I agree, that with the facts you have provided, the Will is likely invalid and the laws of intestacy in the jurisdiction will govern the distribution of Mom's assets. This means that 50/50 is MUCH more likely than the winner take all theory of your sibling.
Find an attorney int he jurisdiction in which your mother lived (and died?) for assistance.
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