I helped a student last year who did have her parent die age 8, then the grandmother die (and that was living in rough circumstances) at 14 and then was in foster care. This was a strong student. Got a couple of top 20 offers and is at one. Also got a lot of rejections, and couple of W/L.
I have no idea what percentage apply. Questbridge was set up to expose low income and students with hardships of the possibilities of going to colleges they might not have considered possible for them.