Again your taking the words "his blood flows within all quincies" too literally. According to christianity, Adams blood (and then noah's) flows within all of us. I just reread the chapter and it doesn't say it literally does. It just says it flows through them all. Inferring that they are his descendants, not children.
And don't come up with claims then say you don't need to prove them, this is a bleach forum, not goddamned christianity.
The holy selection was a technique Juha used to absorb power from quincy he deemed impure. And not every quincy was affected. Ryuuken, Uryuu, and Ichigo all survived. It could mean either they weren't strong enough to provide him power (although Kagiri, a frail girl was taken, scarpping this point) or he left them alive because they would be more powerful later on (similar to aizen letting ichigo 'grow') and may be of some use to him, such as Uryuu coming to his side.