Several elders say, that as per vaastu-shastra or some other treatises:
it's forbidden to keep two idols of Lord Ganesha at home. Further, keeping three idols of Bhagwati Durga or any other Deví is also said to be forbidden. Also, one mustn't keep idols of ugra manifestations of God like Maa Kali, Bhairava, Narasimha, etc., at home. Some even say to not keep idols of Suryadeva too, at home.
Is this belief true? Which scriptures say so? And what all similar rules exists for other divinities?