Why do the game-hops in Kyber and related papers contain 2 steps at a time?
I'm answering my own question here, because i finally found the answer and want to preserve it for future reference.

The Bos et al. paper states it more clearly.
The define the R-LWE problem as a problem on $m$ independent samples, either from the uniform distribution over the ring, or from the R-LWE Distribution where the secret $s$ is common to all the samples.
With this assumption, we can clearly do the game hop with two simultaneously exchanged parameters (here $m=2$).
I am assuming the definition for M-LWE is similar.

Regarding validity of splitting the game hop into two:
That may be possible, but is not obvious, i.e. I was not able to write down the reduction.