In theory, yes, if those shareholders each keep not attending the meeting called by the other shareholder, they could both independently pass or undo each other's actions.
In practice in a hostile situation, they'll be courting the remaining shareholders to gain majority and won't miss those meetings, which tend to also have rules about how quickly or often they can be called.
It is also legal and typical for the bylaws to include poison pill provisions that would automatically protect the existing >33% shareholder, preventing a second >33% shareholder from existing (thus requiring multiple smaller existing shareholders to join forces to overthrow the largest shareholder).
In practice in a hostile situation, they'll be courting the remaining shareholders to gain majority and won't miss those meetings, which tend to also have rules about how quickly or often they can be called.
It is also legal and typical for the bylaws to include poison pill provisions that would automatically protect the existing >33% shareholder, preventing a second >33% shareholder from existing (thus requiring multiple smaller existing shareholders to join forces to overthrow the largest shareholder).