Where did Matthew and Luke probably get a lot of their ideas?

From Mark

Another Answer

Believers are satisfied that The Bible in its entirety was inspired by the Holy Spirit (2 Timothy 3:16), and that its writers were scribes, rather than originators of the material.

Another Answer

Matthew was a direct participant and therefore eyewitness of the events and teachings he described and recorded.

Luke spoke to those who were eyewitnesses. Over 50% of what Luke recorded was different from what others wrote. The content, particularly in the early events of Jesus' life would lead to the obvious conclusion that Mary, mother of Jesus, was one of his sources.

Of course, over all that they wrote was the divine supervision of the Spirit of God.