No. You are asking if you can sue under the powers of a Power of Attorney if you don't have any powers under a Power of Attorney. There would be no 'principal' if there wasn't a POA. You would not be...
No. A stockholder would need to convince the board of directors to vote to take such an action as a corporation. On the other hand, a number of shareholders can sue the board of directors for not...
Lawsuits can be brought by anyone for anything, so yes, a real estate agent may sue a buyer. Now, there has to be a good reason to do so in order for the legal action to not be considered "frivolous"...