What can I do to keep myself from being evicted

Unless you have a written lease and are paying rent, you are a guest and can be asked to leave.  If you do not, an eviction action can be brought and the sheriff can remove you.  The executor's duty is to collect the decedent's property, pay his debts and distribute what remains according to the Will.  Allowing you to live in the house rent-free is wasting the estate and violates that duty.  If the house does not need to be sold to pay your father-in-law's debts and passes to your sister-in-law, she may or may not want to rent it to you.