One could debate the point that the current lending criteria are actually the sort of prudent practices that should have existed all along - requirement to save up deposit etc. So perhaps if Sibling A can't qualify for a mortgage s/he should just accept that? S/he might be able to afford a bigger mortgage right now, but what happens if interest rates rise, taxes rise etc.?
On the other hand, I'm aware that sometimes logic doesn't prevail in lending right now, as I've seen some applications declined that I myself would have approved (if I had The Power) despite my admittedly fairly cautious approach.