Yes but if you do that solution, you won't get dc and there won't be any problem.

That's not what @OsmanAmca said. He said quite the opposite.  

In the middle of the fight if one or two mages from the ally go inside (which means the defending clan has opened the gate for them ) they just call party and they are inside defending all toogether then  its  not csw anymore its nation fight.For months the nation with the most people had been defending the castle fighting againgst one and only clan.The situation has changed last 2-3 weeks since orc side finally balanced the population and now its quite balanced(I repeat last 2-3weeks) But its still a nation fight every individual clan should have the chance to win and compete. We have so many videos of castle transfering last 10 minutes or last 15 minutes or whenever things were getting hard or about to lose they just kept people in the crystal ready to take it before they lose it. As OsmanAmca said even if we remove the ability for the defending clan to close and open gates there  is still going to be the same, eventually the main gate will die quick and someone from the ally will eventually regroup inside so its just going to be the same outcome , im talking for both nations so I dont get misunderstood. If you would ask me for a suggestion I dont really have one I dont think its a management problem. 

At what point during the CSW do allies enter the castle? What if the gates continue to respawn open by default, allow the holders to close them, but prevent them from reopening the gates during CSW?

There may be additional material, I can't think of anything, you are the boss.