Actually, a family income of less than $75,000 should see all of tuition covered by scholarship and grants. As to living expenses, that is in the margins. Keep in mind that the goal of MIT's (and Harvard's, Yale's, Princeton's...) financial aid office is
1) Work out how much the family can afford to pay
2) Take all of that
3) Give the student the rest of the needed sum in the form of grants/aid.
As a result, family income is not sufficient to work out how much the family can afford to pay. The expenses side of that equation is at least as important. The family can have a high income, but expensive medical bills, or multiple children in higher education or something, which means that they cannot pay despite a high income. MIT does draw a line at 75,000 saying that almost regardless of expenses, you get free tuition below that line. Anything else is very much up to personal circumstances.
For very specific questions, the best bet is to talk to your respective assistant director of financial aid. These assistant directors of financial aid (assigned according to the first letters of the student's last name) can assist with specific questions about the financial aid process. That being said, I would not contact them with anything that can be found on the SFS website.
A-Ch Elizabeth Barnes email@example.com
Ci-G Ryan Callahan firstname.lastname@example.org
H-Ld Jason Marsala email@example.com
Le-O Emma Wilcox firstname.lastname@example.org
P-Ss Aimee Yorsaner email@example.com
St-V Susan Wilson firstname.lastname@example.org
W-Z Michael Albano email@example.com