12-hour Watch Swap Question, 28-day hitch

Looking for opinions on the best option(s) for swapping watches mid-hitch.

Scenario: Mariner A arrives at vessel for midnight crew change, having been up all day. Goes to bed, gets up for noon-midnight. Stays on noon-midnight for two weeks +/-, then switches to midnight-noon for the last two weeks. Mariner A is rested and ready for his first watch, and rested and ready for a long, overnight drive home at crew change. Mariner B, meanwhile is on midnight-noon for his second two weeks, and is rested for his drive home. Mariner C arrives at Mariner A’s two week mark for midnight crew change, and needs to get some rest before standing watch.

How do we most fairly and safely get Mariner A onto the midnight-noon?

Is an 18-hour watch for each man the only, or best, option? Spread it out over a couple of days?

Have I made this more difficult than it needs to be? Primary issue is crew rest for vessel operations and for travel. Secondary issue is that each mariner has a fair shot at working days/nights with all that entails.

Feel free to use small words and/or pictures and diagrams. <not good at math>

Over thinking it. Just be flexible on the days you have to swap and relieve each-other when they’re fatigued. A few 4-hour watches could do it with respect to vessel ops. Like slow down the pumps or miss a tide to stay at the dock a little longer.

Ok if you’re crew changing at midnight say 0001 Wed morning then :
Your midnight to noon guy should be the one getting off but
On Tue @ 1800 he gets up and relieves the noon to midnight guy who goes to bed
0001 Wed your day guy is now on nights and has had a 6 hour nap
Your former night guy is on his way home
And your guy that just came on is in bed for 12 hours

Repeat process every other week and nobody gets stuck pulling an 18 hour day and nobody gets stuck the night shift every hitch