In reply to your first question. We all, as individuals and as a community are or should be in a constant state of reform. Reform in this case does not mean watering down, or changing truth, but growing and correcting ourselved when we err. With specific regard to necessity, I would say yes, but possibly not for the reasons you would suppose. Throughout the history of the Catholic Church various ideas have developed that have stayed away from what was handed down from the Apostles, who learned from Jesus what his mission and teachings where. When issues arose, or questions came up there was a natural need to clarify, just exactly what we believe.
To your second question. The problem is not that God made creation imperfecty, but rather that we have free will to accept or reject what God has revealed to us. God desired from the beginning our love to be given to Him freely, not as robots who cannot think for themselves.
As for the both parts of your last question. As Catholic, we don’t claim to know when the soul and the body are united, All we know is that the earliest it could occur is at the union of the sperm and egg. Splitting Zygotes becoming twins, I’ve heard of Re-uniting, into one person, this I’ve not heard of, are you asking about chyronic twins perhaps? Well while the church does not define exactly when the soul is infused (the theological term) into the body, and defaults to the earliest it could occur, and as every life is of value to God, we oppose the direct killing of that life. If there is a real question as to the existance of more than one person in one body, (lets make it simple and use the example of a two headed infant) One “head” is baptized absolutly and the second is usually baptized conditionally, ie, the person baptizing would say, something to the effect of “If you are a second person, I baptize you….” So we always default with the intent of the greater good in mind.