As to why it is believed that Khadija was a Catholic and how the Catholic influence came upon Muhammed comes from a story told by one Alberto Rivera (a former Jesuit Priest) in this video:
sorry ----I cannot do videos----but-----at the time muhummad was active in the business of his wealthy (older) wife----he was exposed to Christians, jews,
Zoroastrians, Sabeans----etc. He was CLEARLY
very much influenced by both Christian and Jewish
theology --------is that not enough ?? Arabia at that time was not "ARAB" It was a busy commercial highway to the east (and back again) and---to the north and west. He also seems to have been influenced by
Zoroastrians------sorta
He stole from whatever he felt like would make him look good or justify his current actions. He was just making it all up as he went along; the Koran is just a load of disconnected, contradictory rubbish. It's not a religion, it's a violent political cult designed for bandits and murderers.