I think you need to ask the schools on your younger daughter’s list, the financial aid director, specifically, on how overseas programs are treated as siblings college for financial aid. St Andrews is a well known university so there would not be any issue in that regard but colleges do have their own methodologies in coming up with how they assess these things. It can vary.
Do fill out some NPCs of schools on your daughters list to see how her having a sibling works, in general, for financial aid at those schools. Then discuss how international schools and programs are counted in their formulas.
thumper1