By your own words, your father's belief and your's disagree. Now most parents don't go around proferring the exact nature of their finances to their children, so on that basis I presume you are coming to your own conclusions without sufficient knowledge.
You say that your mother struggles to earn money: welcome to life... we all do! You say that she works hard and doesn't get paid enough: again, welcome to life... we all do!
Now, all of that in context, you must realize that all people have a different set of values. Perhaps your mother and father have already discussed family finances and determined what they are willing to accept. In that case, who are you to interfere? I most certainly would not let my child interfere with family finances, though I do educate her about managing one's finances.
To be 100% straight forward, approaching your father to challenge his role in the family finances is 100% the wrong thing to do -- it is not your place and it is disrespectful for you to do so.
Now, it is 100% in your place to be confused and curious and want to understand. If you approach him by stating the facts and that you don't "get it" and you honestly listen to his reply so as to learn his thinking without the presumption of challenging him, then you will be doing your "role" (per se) as a child and ask your parent for guidance.
You may agree with his (and your mother's) thinking. You may not. You may even know that your mother's thinking is different. It is not your place to interject. Your parents are responsible for their own relationship and you are not their mitigator. Learn from them; love them; know that you'll occasionally disagree with them, but never think of yourself as appropriate to manage their relationship -- only they can do that.