I’m loving all the contributions to this thread so far.
For the purposes of the story I’ll probably have to find something different to work with, based on these responses, but it’s giving me a lot to think about.
Just keep in mind you can rely a little on magic, I understand you want to keep it reasonably realistic but you do have a little wiggle room.
Venus’s rotation actually has a resonance with Earth: Whenever the two planets are closest together, she always shows the same face to us.
That’s just plain weird … they don’t even rotate the same direction … but plenty of citations on the internet to back up that claim … and I always knew she was a two-faced lil’ twit …
There have been a number of simulations of the weather for tidally-locked planets; some of them show that parts of a tidally-locked world could be ‘habitable’. which ususally means that liquid water could exist there. Some examples have a small habitable zone near the sub-solar point; others have habitable zones near the terminator, where the local sun is always on the horizon.
On a tidally-locked planet with a short year the planet rotates quite quickly, so the atmosphere moves fast enough to spread the heat out more evenly across both hemispheres. Any planet orbiting around Proxima Centauri in the habitable zone would have a fairly short year, and this smearing effect could be quite significant.
I have a suggestion which might just work: make the star absolute minimum mass and have the pair orbit another, brighter star, so the near star eclipses the farther star.
Is that a coincidence or is the Earth controlling Venus’s rotation rate?
Wheelworld. by Harry Harrison, 1980. The middle volume of the To the Stars trilogy.
Wikipedia has an interesting article on the habitability of planets around red dwarf stars that seems relevant to the question, since tidal effects are a major issue.