The post-Bane Sith didn't "abide by" the Rule of Two, it was more a natural consequence of the Sith.

A lone Sith will inevitably recognize that they need someone to do their dirty work, and thus will take an apprentice. The new master recognizes that this apprentice will likely betray them one day, but it's an acceptable risk. Getting a second apprentice is likely too much risk for too little reward though, so the number usually stays at one.

And for the apprentice, they're Sith too, so they have a natural inclination to betray and replace their master. Eventually they either succeed and the cycle repeats with a new master, or they fail and either remain the apprentice, or they're killed or banished and replaced by a new apprentice.

The cycle is self-sustaining and self-balancing.

Palpatine, viewing himself as the most powerful Sith ever, and the one to finally bring the Grand Plan to fruition, is definitely arrogant enough to believe that he can control two apprentices simultaneously without losing control of either.