Let's start with an obvious one. He certainly is not a coward. He was willing to take on a dog that was ferocious; in contrast, Heathcliff makes the comment that the "cowardly children also crept forward..." That quoted phrase is somewhere near the very end.
Your first example of yellow underlining is a wonderful example. Heathcliff is quite common and he would use common English. He characterizes Cathy as being gentile and not given to saying anything contrary to her upbringing.
I would note that Heathcliff followed grumbling execrations and vengeance. [an execration is a threat denouncement or curse. Again Heathcliff is showing his common upbringing. Cathy would choke before she would utter such things. This one is kind of iffy. You could omit it. It is by inference something that shows that Heathcliff is different].
Your second underlined statement is correct. It characterizes Heathcliff as a robber and a thief and part of a lowlife gang. You could go on. Robert does not hesitate to make his feelings known and adds to what you underlined.
Your third underlined statement is correct as well. I have added two but your examples are fine.
Who marks this? Make an appeal if you get it wrong. Interpreting literature is that way. This is not exactly a factual question and the only way to answer it is to compare Heathcliff to someone else. I chose Robert and Cathy. Write your instructor and provide some of the evidence you have provided here.
Textual Evidence. ... But what does the teacher mean about citing textual evidence?' Let's answer that question next. Textual evidence is support for your analysis that comes directly from the text itself.
a word (other than a pronoun) used to identify any of a class of people, places, or things ( common noun ), or to name a particular one of these ( proper noun ).
