I don't think Brown will need to move to the right any to win reelection, his 2018 reelection was something of an analomy compared to the rest of Ohio elections between 2016 and now (he won reelection by an unusually high point percentage). He's generally acknowledged to have a connection with his state's voters that arguably no other Democrat has duplicated (Tim Ryan came close but ultimately it was an upward battle for him, between it being a midterm with a D president and the state's rightward tilt in recent years).
Tester, similarily, has a strong cultural match with his state. While his chances of being defeated are significantly higher than Brown's, he's still not actively disliked in Montana and I imagine he'll be given Biden's blessing to play maverick on certain things to ensure reelection.
Manchin is almost certainly a goner in 2024. Last midterm, R's increased their supermajority in the WV legislature, and Manchin is no longer the senate's deciding vote like he was two years ago. I predict he'll lose to Jim Justice by at least five points, no matter what he does.