The fact of the matter that one should also keep in mind is that unless OP is applying to schools that guarantee to meet full need, going through a lot of contortions to reduce EFC is not going to necessarily generate a whole lot of financial aid.
There is no requirement for his son’s school to increase aid according to change in EFC when a sibling enters college. Most FAFSA only schools do not do that
Most schools do not meet need according to FAFSA EFC, so chances are that the second student is not going to get need as defined by that EFC met. Still, there is more leeway in dealing with the second student by comparing packages and casting a wide net. First student is pretty much caught by policies and practices of the school he chose.