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.
I suggest that you have some fun with College Confidential's SuperMatch: http://www.collegeconfidential.com/college_search/The twins can complete the SuperMatch questionnaire by selecting joint preferences for size, location, majors, etc. Once they've generated a “Results" list, you can check each college that meets all or most of your preferences to see if it will also meet all or most of your financial need. You can also alter the preferences and try again to see what changes. On the second time around, be sure to check the box that says, “I'm interested in schools where I would be well above average, to increase my financial aid opportunities." (It's under the “My Scores" heading.) This will help you to hone in on merit-aid colleges. However, given your relatively low household income and the number of children who will be in college at the same time, you should also do well at colleges that don't offer merit aid but that promise to meet full-need. (Financial aid formulas consider the number of siblings in school concurrently although the adjustments in Expected Family Contribution that each college makes because of this will vary.) Many of the most sought-after colleges and universities offer only need-based aid, but it's usually very reasonable. These schools may be good matches for your twins, but they are also extremely competitive, so make sure that you've lined up “Realistic" and “Safe" options, too. (BUT … one warning: If your income is only $65/70K but you have high assets socked away, you won't do as well with the need-based-aid colleges and will have to focus on merit-aid schools.)
If you haven't done so already, you should also have each of your children complete the FastWeb questionnaire (www.fastweb.com). This will help them to ferret out a broad range of scholarships for which they should be eligible, including (but not limited to) those that are aimed at twins or even specifically identical twins.
Finally, keep in mind that financial aid offers are usually somewhat negotiable. So, after your twins have received their college acceptances, if you feel that the aid that's offered is deficient, you can appeal. When you point out that you'll be sending two freshmen and not just one to this college, you might get a little bit of extra wiggle room that the parents of singletons will not.