What an interesting analysis you have chosen or been given! If I were you, I would want to approach this question looking at the topic of evil and how we are or aren't susceptible to evil in our lives. This to me seems to be the most obvious way we can compare these two excellent texts.
Macbeth, of course, is famous for the way in which Macbeth is driven into acts of murder by the prophecy he has received from the witches and then the encouragement of his life. His ambition is the cause of his increasing evil, that begins with murder and then ends with orchestrating the death of entire families, as in the family of Macduff.
However, let us compare the characters Macbeth and Oliver from Oliver Twist for one moment. Oliver is noteworthy precisely because of his goodness and innocence. In spite of the best efforts of evil characters such as Fagin and Bill Sykes, Olvier remains uncorrupted and an essentially good boy. Of course, critics argue that his character suffers as a result, as he remains a flat, static character, and thus some argue he is unrealistic. However, it is interesting that nothing is able to shake the innocence and naivety from Oliver.
So, this is the way that I would approach this question. A possible thesis statement you could use would be:
Both Macbeth and Oliver Twist explore the concept of evil how outside influences impact, or fail to impact, their central characters.
This seems a really interesting analysis. Good luck!