I would also suggest looking at the Canadian universities, especially McGill. The Canadian universities tend to be less than their US counterparts, and McGill was especially affordable for those who are looking for a BA degree rather than an engineering or CS or other sciences degree. They have different price structures depending on the program of interest, and of course the prices are in Canadian dollars, so you have to look at the exchange rate. I recall when my son was applying, McGill came in at around $30k US for tuition, room and board per year for either a BA degree or for one of their few combined BA & Sc degrees (which is what he was interested in). They also really like high-stats kids and will grant a lot of credit for AP tests, so your twins could possibly graduate in 3 years if they have the AP credits.
Here is a link to the tuition (not room and board) costs. Again, keep in mind that you have to account for the exchange rate, which right now is very favorable to the US dollar.
| Student Accounts - McGill University
And based on my research from two years ago when my son was seriously considering McGill (it was tied for his first choice), off-campus apartments and food are considerably less than US equivalents for a comparable desirable urban environment.