I'd say Brandt and Havertz are quite on par talentwise. Havertz is generally considered the greater talent among the fans though, primarily because Brandt is perceived as somewhat "lazy", kind of like Özil, and Havertz has the bonus of being homegrown. I don't agree with that and think Brandt's really underrated and suffers from the extremely high expectations and our currently rather dysfunctional offense. Bailey is a little bit overrated if you ask me. He had a run of form that caused quite a hype but his technique is not on the level of Brandt and Havertz and his decision making is miles behind both. He's got the best shot and sharp crossing though.
Tah is the same calibre, just as a center back. He was incredible last season and the season before that, I've honestly never seen a CB that good at such a young age and he also improved his build up play. But this year, he somewhat lost his form for the first time and was rightly behind Süle in the NT. Generally, I'd consider him a bigger talent than Süle though. He has everything to become an IV as good as prime Boateng.
You forgot to mention Paulinho, though. We haven't seen much of him as of now but from what I see, he looks special, too. I think the way he moves, runs, dribbles and plays small one twos is very reminiscent of Robben, just right-footed. It is too early to judge, though. Maybe there is only a resemblance in style but not in quality, who knows. But he looks very promising, especially considering that he's 18 right now and even younger than Havertz.
Jedvaj is another case. I think he has the quality to be a CL centerback if he stays injury-free but in his current form, he isn't even good enough for us. I think this level is his ceiling. Retsos though looks like a greater promise in our defense. Had some amazing games for us right after joining and he is also below 20.