You can if everyone agrees that it will not cause problems. I refuse to work with my sister and when she applied management asked me about it and i told them if she was to get hired I would have to be kept away from her.
She wasn't hired.
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Would you like fries with th... I mean, your milk in a bag?
As long as one of you doesn't report to the other one it's okay. I've seen married couples work in the same store. I've seen siblings work in the same store. I've seen parents and kids work in the same store.