Fans in Two Bathrooms Share Power?
Sorry if this don't help but if your asking why are both on 1 circuit, that's because they can be. A bathroom circut for lighting can be top all lighting in both bathrooms that do NOT include a heater. A 3 in 1 fan, heat, light must have it's own dedicated circuit

If this isn't answered by mid day tomorrow, I'll help. If it is, I'll delete this answer. Just sone questions. To assist others and myself later.


What gauge wire is being used?
What size breaker is it?
Have you tested the lines with the breaker off to verify that all lines are dead?
How certain are you of which lines are main supply lines?


Lines cannot be randomly spliced in the walls like your diagram suggests. I would personally use a 12/3 and use the 3rd hot line as a bypass through the switch, lights, and to the next switch. So what you think is upstream could be downstream.

Testing would entail disconnecting all lines, safely cap them, turn on breaker, test lines, turn off breaker, connect the verigied hot line to the next line directly and cap them, turn on breaker, test all lines to verify what line is what and that it isn't spliced randomly, and repeat till you have a definite diagram.

... this may just be me... but please also clean up diagram as power in, number of lines,  and where you want things. The "whatwass" and "what will be" party makes it hard to follow.