Jesus pbuh himself said:
considering the following verses:
Matthew 15:23 But Jesus did not answer a word. So His disciples came and urged Him, “Send her away, for she keeps crying out after us.” 24
He answered, “I was sent only to the lost sheep of the house of Israel.”
He made an exception for the woman concerned in the passage, as she had a smart answer for him.
Also considering the following verse...
Hebrews 1:2 Hath in these last days spoken unto us by his Son, whom he hath appointed heir of all things, by whom also he made the
worlds;
Could you tell me which
World is
John 3:16 referring to?
Crucifixion, Trinity and Resurrection are all disputed from Christian sources, I do not even need to quote the Qur'an. Why would Muhammad pbuh want to go against the core Doctrine of Christianity? Far easier to have aid, yes he was crucified, but before he returns I am the promised comforter, or a Prophet sent to make things ready. Much easier, and would have attracted much more reverts, much quicker. Clearly he spoke the truth as your own early sources confirm.
As for Isaac and Ishmael pbut both, they were both part of a covenant with God, so I'm not sure what difference it makes? The story of Isaac pbuh and the sacrifice does not add up in the Torah. Jeremiah 8:8 comes to mind.
Muhammad pbuh was not a liar, but both Peter and James, the family and Companions of Jesus pbuh considered Paul to be a liar and likely the false self proclaimed Prophet mentioned in Rev 2:2.