This could get very complicated.
Several issues are posible. Sis will need a lawyer to succeed on them.
First common law marriage.
Did the two ever live in one of these states:
If yes, they may be married and not know it.
If daughter agreed with the other heirs and person to the desired disposition, then she may be bound by contract law.
Next, contract to make a Will. Sister may have lived with him so long BECAUSE she understood that he would leave her the estate. Detremental Relianse as the law calls it, may get the Court to create a Will for her.
When can they force her out of the house?
A Not for a while. They would need get a probate going and try an eviction. But sis can seek relief as a dependant of the deceased, in California it is called a Family Allowance - being family is not required. It wopuld be in the state's probate code.
Does she have a time frame that this could occur?
A. 30 days min for a probate then eviction time maybe another 30 days.
There is no will. How long does it take to get appointed executor of the estate. A. 30 days absent an emergency (can be one day, but not likely here)
Does she have to give the daughter keys to the house if she is still living there? A Absolutely not.