So I just read the entire thread - and agree - the FAFSA, other than perhaps your state school, won’t help. Most OOS schools don’t offer substantial need (UNC, UVA are the only I believe) and many privates will have CSS requirement. Having kids in school simultaneously could help but it seems like the kids are spread apart and maybe would only have a year of overlap.
What not to do - try and game the system.
Rather take advantage of the schools that offer big bucks. For a 3.5 and decent SAT/ACT, you want to look at schools like Alabama, UAH, Mississippi State, Murray State and more. For a 3.75 or higher, U of Arizona. A lot on here like Iowa State - some have described it as a mini Purdue. The Florida state schools, not easy to get in, but are reasonably priced - Florida, Florida State - with a strong ACT can be really cheap, UCF, UFS, FAU, etc. Others mention, Utah, New Mexico, South Dakota School of Mines, Mizzou, Arkansas, Missouri Sci & Tech.
Really need to know actual #s (not pretty good or decent student), desires, and how much does money matter…so if the student wants to be in a certain region, but for $30K all in, they’d go anywhere - that type of stuff. Also, other interests - because half of kids won’t finish in engineering (if that’s the major of choice).
For your son transferring - again, a low cost school might be the way to go- and there are some - but what’s the desired budget?