If your mother passed away and your stepfather you've had for fifty-five years puts your half sisters name on his 401k and insurance , he has cancer. Is she entitiled to it . Nc.

Is my half sister entitled to everything if there is no will and my stepfather of fifty five years puts her name on 401k and insurances, he is dying of cancer and my mother already passed

You have no claim to a "step father" inheritance. He is not related to you legally in any way
Without a will you would still not get anything, with a will you will only get what he leaves you, if anything

At least in the US, if her name is on the 401K and insurance it does not even go into the estate.

Now did you receive anything from your mom ?