Ishida is more than just half quincy. His dad was a full quincy, and his mother was a diluted quincy. So he's really like 3/4+ quincy.
Ichigo and family on the other hand is straight up half quincy. And there's probably a reason they didn't all die during the Purge or whatever - either the Shinigami blood in them protected them, or their quincy blood is too diluted to make a difference. I don't buy for a minute that Juha "let" Ichigo alive. If he really had the ability to wipe him out then, he'd just do it now, or once Ichigo shows up to challenge him. I think that was just a fear tactic he said to Ichigo to underwhelm him.
I think the Vandenreich is composed of nothing but 'spirit' quincies. Though the point you made about Ishida's father is valid, and honestly has to mean something down the road. Did Ryuken successfully hide from Juha's radar? I doubt even stoner Kubo would make a fuck up like that.