Again, I maintain that if the WG starts bringing EVEN MORE people into this situation, if should solely be a display of overwhelming force to one sidededly crush our side and functionally win. There is literally no reason to just piecemeal bring one or two people here just for them to ALSO lose, extending the arc more for no actual purpose. If Oda wants to bring reinforcements then he should just have Shamrock pull up with the whole HK roster (to introduce the current day HK's squad properly), and some of the Gorosei (or as you said, maybe at least Garling) and they just overwhelm us and run us off the island.
Otherwise, what would be the point? Just to give Sanji and Zoro opponents that are more of a challenge? That's boring, and doesn't really serve the plot imo. I don't think Zoro or Sanji would really stand a chance of beating Garling or Shamrock right now regardless.
It depends on the current situation. I think Imu has other God's Knight deployed, and that the Gorosei are going to be busy with Blackbeard attacking. I also wonder if Teach can actually cut off teleportation to Marijoa by covering it in Darkness...
I kinda do hope the whole God's Knights are deployed, or most of them. Gorosei stay behind to protect Marijoa, Imu summons the whole God's Knights.
I have the Red Hair Pirates, Mihawk, Kuzan and possibly other Blackbeard Pirates, Rayleigh + Shakky + Boa, and Zunesha + Law coming to Elbaph, here. So, I think there would be enough people to fight.
Also, it's simple observation of the battlefield: if Killingham and Sommers can't handle Zoro and Sanji due to CoC, Imu needs to summon in people who can handle them. And until Imu is kicked out and the Magic Circles are destroyed, the Gorosei/God's Knights will be able to be summoned back into the country.
Like I said in the beginning, I do wonder if Imu has deployed God's Knights to other places than Elbaph. Alabasta, Kamabakka, Dressrosa, etc. They still have to deal with Leo and Sai trying to kill Charlos.