Your visa officer might put you to a question regarding your father’s income. Do not get worried, but just read Richard’s suggestions to answer the question.
In such a situation if your father’s income is low then go ahead and accept the same. But don’t stop there says Richard. Continue that though your father’s income is low, your family income is 25 lakhs or 20 lakhs. Explain to the officer saying that your mother, sister and brother are also working which the officer is not aware of. For example if your father earns 6 lakhs per annum and if you are asked such a question, then you clearly state that since everyone in the family, mother, brother and sister are all working and their annual income exceeds 25 lakhs and they are all supporting you in your education, it should not be a problem at all.
On the other hand if no one from your family is working except your father you can justify saying that your father has been working for more than 30 or 35 years and he has been saving for your education all this while. So even though he earns less, he already has funds saved to support your education. You can also mention that you have your education loan as well to support your stay and study in the US. Richard insists never to blindly accept what the visa officers tell you, but justify that your father has enough savings and to add on you have your bank loan. This would convince your visa officer and get you the visa.