Despite my previous posts, some here keep recommending going to the authorities over this matter. Fortunately, Wordyword has already wisely decided to avoid this action. For anyone in similar circumstances, educate yourself before you contact authorities and potentially initiate conservatorship proceedings in probate court.
Going to the authorities in the manner that some have suggested here can result in the court appointing someone not of your choosing to serve as your parent's conservator(s) (there are conservatorships of the estate (financial conservatorship) and the body (conservatorship of the person)). That person/entity will most likely receive court-ordered compensation for being a conservator ofyour parent's estate and/or person. The conservator could also be a county agency or a private fiduciary that provides conservatorship services. The court could also impose other restrictions, some of which could be sought by your parents, including forbidding you from visiting, etc.. One thing is very certain; a conservatorship proceeding will be very expensive for your parents, and they will have no choice but to pay all the costs, including the costs of the county's counsel, who will likely be a party to such proceedings. There's a real good chance your parents will hate you for the rest of their lives for the radical change this could cause to their lives and happiness.
For those who have made the recommendation to go to the authorities without first seeking legal advice, please learn more about conservatorships before you ever make that suggestion to anyone again. If ever there was an issue warranting spending money on an attorney, conservatorships/elder law is it.