Generally I don't like to discuss my own threads but this is interesting.
In the case of Senjumaru we have that she shook 3 worlds while she was in the Reio's palace, in another dimension for practical purposes, generally shaking a planet is a continental feat, a little more or a little less but there is one more piece of information that must be added.
In Bleach, breaking the balance means that the three worlds come back together, we know this when Ichigo stabs Reio.
Merging 3 worlds (the size of Earth) is a planetary feat, minimum 150 Zettatons if we want to give it a number.
We have the background that Zero Squad has a blood pact in which they can only release their true Reiatsu level when three of the four have died because if two or more release all their power they risk breaking the balance, that is, if more than one of them releases their power, that disaster would occur.
So... if two RG = Planet+ level then one RG would continue entering planetary levels, at least that is what makes the most sense taking all that into account, if they only shook the planets, they would not have such a pact and all of them would have used their bankais at the same time.