All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Your uncle is in grave danger for practicing sorcery, telling lies to others, backbiting them, harboring malice towards them and not acknowledging his duty to maintain kinship ties.
Sorcery is nothing but lies, falsehood and deception. It may also involve soothsaying, which is an act of disbelief in Allaah The Almighty.
By saying, "He does not acknowledge maintaining kinship ties, nor acts kindly to his relatives," if you mean by this he does not admit that it is obligatory for him, then you must explain to him the evidence for this obligation and inform him that the person who denies it after being informed beyond ignorance and doubt is committing a major act of disbelief, which renders him an apostate. This is because he has denied an undisputable obligation in Islam that every person is aware of.
If he does not maintain kinship ties, fulfill the rights of his kin, or harm them, while admitting that it is obligatory for him to do these deeds, this is a major sin. The doer of such misdeeds may bring upon himself the curse of Allaah. Similarly, backbiting, bearing malice towards others and telling lies are all major sins.
As for how to deal with him, you should consider what is best for him. In other words, you should shun him and warn others against him if you feel that this is better for him and will help him give up such evils. On the other hand, if keeping closer to him, advising him and instructing him would be beneficial are useful to him, you must do so.
And Allaah Knows best.