Hello.
I propose something very simple. If they enlist to participate 10vs8. So the conquest is 8vs8. Therefore, two players from the fleet that listed 10 will be left out.
Those two players should be substitutes.
Why alternates? In case, in the beginning of the conquest, their connection drops when they go down to the planet, which is why it does not allow them to go down and participate, then they can be replaced by the substitutes instead of the holders.
Because disconnections at the beginning of the conquest and the conquests at a disadvantage in number are very normal, it is not fair or fun for both parties.
Best regards.