How can we go about getting Power of Attorney for our Father with Dementia?
Others here have said that his having dementia means he does not have the capacity to sign a valid power of attorney, but that is too categorical. Dementia is a continuum, and the cutoff point where someone with it is considered incompetent to sign a valid power of attorney is NOT at the point where he or she first begins to show the signs.
Given that there is at least one person likely to challenge any POA your father gives you, I think you'll be wise to hire an elder-law attorney (in his state) to help you with this. An experienced elder-law attorney may be able to advise you, after meeting your father and talking to him for a while, whether he seems clearly capable, clearly not capable, or close to the line dividing competence from incompetence, and can probably advise you on what steps you can take to clarify the issue, such as getting one or more doctors' opinions. If it's a go (if your father is still sufficiently competent), the lawyer can also write up a good POA that gives you the powers you will need.