OP is not going to receive merit aid at Northwestern & is unlikely to get any at WashUStL, yet they are OP’s top 2 target schools. This leads me to believe that OP’s parents would like merit aid, but that it is not necessary. If it was, then many large state publics would / should be on OP’s list as should lower cost Rice University.
“not comfortable” paying $70k plus per year is different than “unable” or “unwilling to” pay above $70,000 per academic year.