Well, I think that for the first question, a biological pathway can help to find interactions between gene products (proteins) and how these interactions are involved in the disease.
For the second question, I think that finding gene families with specific functions can give us an idea of the cellular processes involved in disease.
I do not know if I am correct, I have read but I have not been able to clarify the ideas. If you suddenly know of papers that can clarify these concepts for me, I would be grateful.