Initially, he views the Christians as crazy but harmless, as they talk about a man with a mother but no father. Further, they speak funny and the villagers make fun of them.
After some of the villagers and then Nwoye converts, he sees them as more of an evil that need to be uprooted.
Okonkwo wished to drive the Christians from the land.
Okonkwo grinds his teeth in disgust at the decision to only ostracize the Christians instead of drive them out forcibly.
Okonkwo disowns Nwoye when he converts to Christianity. Okonwko originally assaults Nwoye when told of Nwoye's association with the Christians, resulting in Nwoye leaving the compound and joining the Christians.
No such event happens. However, Okonkwo does argue against leaving the Christians alone.
Okonkwo wants to violently force the Christians out of the village with whips.
Okonkwo disowns Nwoye after he joins the Christians, claiming Nwoye is no longer his son, no longer his children's brother. Okonkwo tells his children, "You have all seen the abomination of your brother."
Nwoye was seen associating with the Christians. After being threatened by Okonkwo, he joins the Christians and volunteered to go to Umuofia where a school had been set up to to teach young Christians literacy. Effectively, Nwoye had abandoned the gods of Okonwko and his fathers.
Ezinma is the child who is most able to understand Okonkwo's view points and what he wishes for their family. She seems to share Okonkwo's desire for family honour and is willing to sacrifice for it as well.
Christians view owls as one of God's wonderful creations, so most Christians are okay with them.
The holy animal is the giant royal python.
Subjective answer: The thing that upsets Okonkwo the most internally, is the fact that Nwoye is too much like his grandfather Unoka. The one action that gets Okonkwo the most upset externally is finding out that Nwoye has been hanging around the Christians, at which point Okonkwo confronts Nwoye and nearly chokes him to death.