Page and Brin are not married to each other, as far as I know (which would make the shares their common property). You can always try to drive a wedge between them, have one of them turn on the other. With Zuckerberg, no, no chance.
They are both basically retired so there's not much to wedge about.
Although the parent is downvoted his point is valid , individually brin or page does not control 50 % of voting rights as zukerburg so alphabet has slightly better structure than Facebook