Our younger one scored just below the mark in the WPPSI, given that English is her second language, we expect she would qualify after a year or 2 of full time school versus a couple of hours of preschool. However, it would be very hard for us to manage IF she doesn't qualify eventually. I think that if your YS' needs are much more extreme than siblings, then it is easier for everybody to accept and deal with it.
All I have to say is SBV. It's very painful to watch the oh so close WPPSI score especially if your older child is in. BTDT including the bilingual part and then qualifying SBV

Now if only I knew his WJ-III results.