Just keep in mind that the more complex your own financial situation is, the less reliable the NPC estimates. So unless your son ends up with his heart set on the ED 2 school… to the extent that all parental figures are willing to pitch in and contribute something more than originally anticipated… it may just make more sense all around to go with RD.
The situation I worry about is one where a family walks away from an ED admission with a disappointing level of aid, only to find out in April that all options are worse than anticipated.
So my point is that you need to be very certain of your own willingness to bite the bullet and pay for that school before allowing your son to apply.
The reason schools encourage ED is that it is beneficial to the school. It allows them to pick and choose students who meet a variety of different admission goals, knowing that those kids are going to come.
The admission goals shift as the admission season progresses, so it is quite possible that particular traits of a given applicant are more or less advantageous to admissions during different phases. You can’t know what those admissions priorities are or will be, but you can at least be cautious about buying into the notion that the ED process gives your student a huge boost in admissions chances. The numbers that show an ED advantage reflect group averages, not necessarily applicable on an individual level. And schools have to admit enough RD students to cover their yield…that is, if there is a 50% yield on RD, the school has to admit twice as many RD students as it needs to fill the class.