Wash U is not a flagship. It is a private university. Do you mean they chose a large flagship instead of Wash U?
But back to the OP. These twins need to visit some colleges of varying sizes and locations. They will have a better idea of what they like if they do. AND remember, they are just beginning their sophomore high school year. A lot could change in terms of their desires and interests between now and fall 2027 when they do college applications.