What is the language in the will about who gets the property after the life estate is over?
You probably didn't know it then, but if there was a question about your parents' mental competency, that should have been tested while they were living and it could have been a major factor if either will had been written after they had been diagnosed as incompetent. Did your sister acquire conservatorship through a court proceeding and is there medical evidence in medical records of a diagnosis of Alzheimers/incompetency by a physician? You might have had grounds to contest the will but contesting a will is very expensive in legal fees and it is questionable whether that would be worth it to pursue due to the limited value of this estate.
You were extremely lucky to receive the payout from the insurance policy. If you know the names of the other insurance companies that paid her, you should contact those companies by letter to inquire whether she used her POA to have the beneficiary designations changed at any time--if she did do this, then this was illegal. Assuming that the insurance companies will even give you any information, if you do find out that she did this, then you will want to hire an attorney who specializes in insurance actions to consider filing a lawsuit against her and/or the insurance companies. But please also be mature enough to realize that if you were not named as a beneficiary on any other other policies that you are not entitled to anything from them, even if the will says "all assets are to be split 50/50", since the beneficiary designations override whatever the will says.
Since we can't see the language of the will, the people reading a message board would not be able to give you a professional opinion about whether this estate was handled correctly or not. Ask a probate attorney to examine the file to see whether or not you have a basis to recover anything else.