If your sister paid rent, she was a tenant. There are laws to protect tenants, but those depend on what country, state, and city you live in. In most places in the US (maybe all), she was owed more than 2 days notice. Normally, the local housing authority could help her figure out what her rights are, but since this already happened, they may not be able to do much (depends on the local laws). It's worth asking them anyway. I don't know how partial ownership of the property would affect things if your sister was a partial owner.
If the 30 year old will was the most recent document, then that's how the estate will be distributed. There are no laws in the US requiring a will to be fair. An executor's role is to carry out the will. Being an executor does not mean one can choose to unilaterally sell the property in the estate without permission of other heirs. You'll need to speak with a lawyer if you think they're breaking the will by selling property that you have partial ownership of. But since the sale is already done, reversing it would be slow and probably very expensive in legal fees. If it's a small estate, you'll have to judge whether a lawyer is worth the money and the family's animosity. Also, if the estate had debt, debt must be paid before property is distributed to the heirs, so that could also change what your sisters had to do.
I'd suggest first asking your sisters to tell you about what they've done to execute the will, and what they do in the future.