知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。 Hence 'are Either of you free?'should normally be correct. Nevertheless 'Is both Peter or Paul free?'could be accurate, since either is the opposite of 'both' and that's why the conjugation 'is' would be accurate in these types of instance. It’s Specially widespread in reference to, e.g., the https://sexeslive.com/