Hi there!

This mod can help indirectly.

The main part of the solution involves determining how to achieve the effect of "buying items from station X and then sell them..." etc. Here I recommend using the Mules, Supply and Warehouses Extended mod; details will be omitted here, but that mod should be useful.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2013772865

Then, the remaining part of the solution finally involves this mod. Since MSWE is supported by this mod, it means you can do the following:

1. Pick any one of your small ships; that ship will become the fleet leader later
   
2. Set the MSWE default behavior onto that picked ship (check their docs on this)
   
3. Select the remaining other small ships
   
4. Assign to the picked ship: Trade For Commander
   
5. Finish!

What happens next is that this mod will notice this special assignment and then automatically copy the leader's default behavior to the fleet members. Later, you will be able to control what the entire fleet should do by simply modifying the default behavior of the leader ship.

Edit: formatting