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I will try and help. You will need to sit down with a local attorney and lay this all out. It may be a difficult battle, but you can possibly prove a case for undue influence which is a form of elder abuse. Keep in mind, unless you were present for everything you outlined above, they will likely have a very different story. Most attorney's will consult for free and, if you have a good case, might take it on a contingent fee basis.
I hope this helps.
You want to talk to someone who handles elder law/elder abuse. If something improper happened here, that is what it is.
Best of luck to you.