230 volts 50hrz boat with shore power and generator with a separate AC source panel and AC Distribution panel.

I am installing 2 MultiPlus 1600/70 unit in parallel (location constraints close to the battery bank made it optimal to install 2 smaller units).

Question: what would be the optimal wire size to run from a: The AC source output to the multiplus(s) and b: from the multiplus(s) back to the AC distribution panel?

The distance between the panels is approximately 3-3.5 meters one way. At what point would you add the junction box to split the AC in wires, the AC out wires and would you keep the same wire size throughout.

Thanks in advance for any advice,