I expect the youngies to turn up once we're inside their attention span. We have a couple already, but as you point out, people under 30 dont usually plan 18 months into the future :D.
This is a not to be missed trip, stick a reminder in your diary for about 6 months from now and then take another look. I promise you we'll have people on board so you dont think you're traveling round India with your father-in-law ;).