Good for the girls. I wonder if they will go to boarding in Canada like their father did for awhile.
I don't think they will go boarding overseas. Both Felipe and Letizia are much more hands on parenting than JC and Sofia were and Letizia loves and has been brought up in a different environment and closer family unit.
It's highly likely though that Leonor will complete a Masters in either in Canada or USA as part of her broad and diverse institutional education. First questions are being raised about her education which hopefully will be answered in the next couple of years.
I don't think attending boarding school, is so much about your parents being a failure, but more about becoming independent. Therefore, if it shouldn't be a school I can certainly see them making a gap year or maybe some charity like Elisabeth of Belgium recently did.