If your father signed valid DPOA forms, then your brother could very well have the right to block your access to the property. Your recourse would be to file an action with the probate court to become your father's guardian/conservator. This would effectively "trump" your brother's authority under the POA forms, if a court agrees. This is likely to be contested by your brother and you would certainly want to retain an attorney to assist you.
Another option, if your father still has capacity, would be to have him sign NEW DPOA forms, revoking the prior forms. Of course, that could lead to a lot of back and forth yo-yo-ing.
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Another option is guardianship if yiur father is incapacitated but your brother's POA appointment might resukt in the court appointing your brother as guardian; if instead a new POA appounting you then you might have preference. Sticky wicket, but whoever is in charge has autority to chanfge locks/lock out; get advice and assistance of an attorney ASAP.