Right.... eh. There are people who went Guano Crazy (that is technical jargon for totally kook-koo) over this murder. So their being employed at a certain place could result in people showing up and interrupting the business. It could even put the other employees in danger.
So I can understand why they did it even if I am not convinced it is right.
I think the kohberger family resides in a small town where everybody knows each other. That could cause severe problems for the business employing members of family.
So yes, my sympathies are with the sisters if they had nothing to do with the horrible crimes of their brother, but we still live in a capitalist system, and private employers are allowed to fire any employee for business reasons.