re: Consolidating estate of parents in declining health

Your MIL needs to consult with an estate planning attorney. He will be able to help her arrange her affairs to prevent acrimony among family members, by spelling out your wife's role in administering her affairs, while making sure her estate is utilized in the manner she desires. If set up properly any estate tax tour MIL might owe can be deferred until your FIL passes away.

Do the same for your father to get the necessary documents allowing you to make decisions on his behalf.