Can I take over my father's power of attorney if someone non related is his POA right now?

You need to pursue it through the courts. You should consult with an elder law attorney who has experience with financial (or other) abuse of seniors. A 1- or 2- hour consult with such an attorney will tell you whether you have enough evidence to proceed, or what evidence you need to provide. I'm not sure you can pursue guardianship without representation, and the laws differ from state to state. This is another good reason to see an attorney.

You cannot just "take over" dad's POA. That assignment is his choice. If he is incompetent it is too late for dad to make a reassignment. You would then have to pursue guardianship and show the POA is not acting in dad's best interest. The court is unlikely to assign a guardian different than the POA unless there is evidence of actions not in dad's best interest.