How do you maintain the "treat others with respect, keep it professional" culture without getting into a position where some team members become sensitive to any amount of criticism, and the focus becomes more about not upsetting people rather than genuinely caring to provide kind but constructive feedback and move forward?
Basically, how to you strengthen and guide this part of it:
>When Joe proposes something and Jane disagrees, it's on a professional, technical level. Joe knows this and responds in kind.
Either you need to work on how you deliver the message, or your manager needs to handle the other team members as difficult.
(Assuming that you're not rejecting pull requests with "this code sucks,") It's time to escalate the problem with management. Otherwise, you need to plan to spend more time mentoring, and/or find another strong member of the team to split the mentoring with.
Basically, how to you strengthen and guide this part of it:
>When Joe proposes something and Jane disagrees, it's on a professional, technical level. Joe knows this and responds in kind.