There are some colleges and civic organizations that advertise special deals for twins. (See http://www.twinstuff.com/college_scholarships.html ) But I don't think that any of the twin scholarships in the Northeast will offer what you seek (e.g., George Washington U. has a half-off deal for a second child when parents pay full freight for the first but you'll be eligible for a lot of need-based aid and shouldn't have to pay the total cost of either tuition; Wilson College in PA offers a scholarship of 45% tuition when both twins enroll. But this small, struggling, newly coed school probably isn't a great fit for your top-decile children).
Thus, “The Dean" advises you to look for a college that meets full need for all applicants with minimal loans and/or one that is likely to lure top recruits with merit aid, regardless of whether or not they show up with a sibling in tow. Given your situation (one child already in college; two strong students about to go; a couple more waiting in the wings) and a low (by college-tuition standards) household income, the “identical twins" factor should not loom large in your college search. More critical will be finding a place that both your current 11th graders will love that is also financially stable … and generous. Because your twins are excellent students, there should be many options that fill the bill.