I applaud your ecumentalism here, but how do you fellowship with those who adhere to a LOT more 'doctrine' than what you've written here?
Good question. I believe the Apostle's Creed is a good summary of what Christians believe. However, as I state in other posts, just as people and churches can skew and misinterpret scripture, they can do so with any written word to justify their beliefs. There are so-called Christian churches that I would not consider Christian. Among other false doctrine, the Mormons teach that Jesus had “inherited divine powers” from the Father. Mormons deny the historically Christian teaching that Jesus Christ is equal with the Father in essence and substance. Jehovah witnesses do not believe Jesus is the Son of God.
One might ask, "At what point do we not have Christian fellowship with another person"? By "not have" I do not mean shunning any human being but rather the inability of my spirit witnessing with another person's spirit - that they are a born-again Spirit-filled Christian. I.e., judging by the Word and spiritual discernment. How a person perceives Christ in the scripture and whether they have communion with Him in their heart witnesses to me - confirming in my heart that they are followers of Christ, i.e., they are Christians. A Christian's Spirit of discernment needs to be exercised. We can only be born-again when we receive Jesus for who He was and is according to the scripture and I would add, traditional orthodox (small o) church, teaching about Christ. Apostle's and Nicene creeds come to mind.
In summary, any church or person who diminishes or skews who Jesus is past, present, future according to scripture - is not saved and therefore impossible to have fellowship in Christ with that person. Why, because the Spirit of Christ is not abiding with that person. Religion, doctrine, quoting scripture, argument - do not equate being born-again and filled with His Spirit.