They may have sold or assigned their interest to the corporation, which includes the right to sue. You would do better talking to a corporate trial attorney.
There are a whole bunch of moving parts here that I don't know, so I can't give you a good answer. The first thing I would have to know is what happened for you to have done all this research. Are you trying to sue them (it's not 100% clear from your question)? If so, what was the cause of the original dispute? We'd have to have a real conversation for me to be able to sort this out. You do need a lawyer to straighten out this mess, though.
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You may want to refine your question. Nowhere in the information you provide actual facts that led to the dispute, and the reasons why the corporation is suing. The determination of whether the corporation has standing to sue will depend on the facts leading to the dispute.
I would urge you to refine your question, so that my colleagues and I can attempt to address it.
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