I have three questions: 1) Is it Haram to eat and sit with Qadiyani people? 2) Is it Halal to divorce his wife in her period or pregnancy? Is it counted as divorce? Is saying three divorces in same moment and take her back right way and ask forgiveness to Allah permissible to do between couple? 3) If some one dies can we read whole Qur'an for that person?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

No doubt that fellowship has a great positive or negative influence upon every human being. So many people repent and return to the right path due to good fellowship and vice versa; others go astray due to bad fellowship. So, a person should take virtuous friends.
However, there is no harm to be a companion of people who are not virtuous for the sake of inviting them to Islam or for business provided that you leave them if they start to make any form of fun of Islam and so on.
Allah Says (interpretation of meaning): {And it has already been revealed to you in the Book (this Qur'ân) that when you hear the Verses of Allâh being denied and mocked at, then sit not with them, until they engage in a talk other than that; (but if you stayed with them) certainly in that case you would be like them. …} [4: 140].
Here, we clearly state that Qadiyani sect is non-Muslim. Then, whoever looks into their beliefs, will have no doubt that they are not Muslims.
For more on this sect, please read Fatwa: 82809.
Allah knows best.