Is is feasible for us to pursue Guardianship for our father who has Alzheimer''s since we discovered our stepmother has been stealing?

Father diagnosed with Alzheimer''s 5-6 years ago. When he was no longer able to remember day to day, stepmother took him to a lawyer (not his lawyer) and had the will changed to disinherit everyone and leave everything to her. She used him to refinance mortgages on her rental properties. She had Dad cosign a loan for a vehicle for her son and cosign for his apartment. She had him cosign a car loan for her daughter, car was repossessed. She got a credit card in his name and uses it for items for her rentals. She has access to his checking account and his account is overdrawn and she uses his overdraft protection like a loan, not paying more than the minimum. She got access to his investments and has been taking thousands out and sending it to her son. She has been telling us for years that she has no money and can''t afford to pay for Dad''s medical care or for respite care, but we discovered his care is not that expensive. There is more that I can describe here. Help?