Why do some elders say not to keep Mahabharata book at home and not to worship some specific God forms at home?
It is quite a superstitious belief that keeping Mahabharata book at home or reading it in totality will bring a split (or fight) in the family. Since Mahabharata deals with the grand Kurukshetra War between brothers to claim ownership of the Kuru kingdom, this sentiment might have come. During my boyhood, when I was reading Mahabharata, my mother would warn me and advice me to skip a few chapters!
Unfortunately such a superstition has distanced many of us from going deep into the Mahabharata story which is so full of teachings and morals that are so apt for our generations too.
It is normally advised that ferocious God forms (particularly Kali, Tara, Dhumavati, Chinna Masta, Chandalini and the like) are highly discouraged from worship at homes. Sri Ramakrishna Paramahamsa used to say that unless there is a wherewithal to follow regular and prescribed worshiping procedures (as per tantra shastras) at home, it is best to avoid keeping images/ pictures of such goddesses as they have the potential to harm the owners.
In the recent past Mata Amritanandamayi (Amma) too used to take away such pictures of goddesses if found in the pooja rooms of her devotees when she made house calls based on their invitation.