From another mom – we set clear financial parameters around kids’ process and decisions – we are fortunate to have about 80% of the cost of typical, private school costs covered, and we were clear that we could NOT take on additional indebtedness for their education (or shed assets). So, one went to an excellent public flagship where he had everything he wanted and more, and the other applied only to safety/matches in order to get merit to close the funding gap. They are both happy, and receiving excellent educations, with tons of opportunities.
Every family has to identify what is right for them, but our kids did not apply anywhere that we didn’t already know we could afford. Your younger kids, unless they live at home and start at community college, are going to have substantial college costs as well – maybe not quite as expensive as Duke, but still substantial. Personally, I would caution against maxing out for 1, and then feeling stuck with the younger ones.
As for engineering, there are many folks here at CC who can advise about engineering programs, I’m not one of them. But it does sounds as though the “perks” of being a top 20 grad for an engineer flatten out.