We need to fix the 3rd issue first. You can use an analysis group to host the structure and the monitor at the same time. Please refer to this example: https://optics.ansys.com/hc/en-us/articles/360042097393-Metamaterial-parameter-extraction-Smith.
The monitor can use the structure location information once you define and use the parameters properly.
Once all the four monitors are in the same analysis group, you can manipulate them to give output for optimization. In the optimization, you specify the FOM inside the analysis group. for example, if you want to get the averaged E-intensity from 4 individual monitors as FOM, you can
this "fom" will be in the output of this analysis group, and the optimization can find this data from this analysis group.
It is also doable when the monitors are not in the same analysis group. Then you will do the fom calculation in "model" script, which has the highest pripority in the project file. and you can also set the monitors to change with geometry in "model". This might be better as you do not need to have a large analysis group. The photonic crystal examples might be good for you to refer to: https://optics.ansys.com/hc/en-us/articles/360042038213-Bandstructure-of-planar-photonic-crystal-with-a-square-lattice
With this, you can include both S and P polarization from two simulations.
I believe this will resolve the above 3 issues you are facing. In case you have questions different from the original, please write a new post.