What can I do if I think my dad's ex fraudulently got in his will right before he died?

For 17 years dad and step mom had a post nup. 9 months before he passed he put her in the will and trust. She is now getting 1/3. His health was not good and seems very weird that 17 years post nup in place, he would suddenly do that. Two years before death he amended his will to exclude an heir that stole from him. He said in that amended will that this does not change in anyway the post nup. A year later he says in the new will she is now a trustee and personal rep of estate and trust. She was getting $750k or so, now it seems she is going to get $10 mil. He passed 9 months after these changes were made. Seems to coincidental to me. Is this legal? Is there a provision that x amount of time must pass? I need help. She is also trying to now take the house my parents built and that She " never liked" anyway. As well as other nominal $$$ allowed by such. We are in Florida.