What characteristics of Dunstan are brought out through the incidents in Silas Marner?

I understand that you are referring to Chapters 3 and 4
where you see the majority of the references made to
Dunstan.

From the incidents that occur, we see that Dunstan
dominates is brother because of his conniving ways. He is idle, malicious, and holds
over his brother a debt incurred by himself. He demands that his brother does as he says
and pleases. He now put his brother in the awful predicament of selling his only horse
in exchange for money they desperately need. Hence, what we get from the incidents is
that Dunstan is not to be trusted, is mean, and disrespects those around him, whether it
is family or not, and that he has the potential to really hurt someone when things do
not go his way. He is heartless, and quite evil.