One Monster - One Weapon Per Action?

Can a monster that has multiple actions in a volley declare a different weapon for each action? For example Maneuver+stony grip followed by Attack+vicious bite (assuming that activates a special ability)?

Or would the monster need to have “stony grip” equipped for the entire first volley and, assuming the PCs didn’t break the grip by the second volley, equip vicious bite to try to activate the special combo?

Along a similar line, could a character acting twice in a volley pick a different weapon for each action (e.g. PC1:Attack+Sword, different PC action, PC1:Defend+Shield)? This is assuming 2 or fewer PCs in the conflict of course.

I like the idea of the monster needing a new volley to switch weapons since it suggests that a volley is a flury of activity that doesn’t allow for changes in tactics, plus it gives players time to react (the halfling has been grabbed, do something!).

Curious how you all have handled this and/or if the rules spell it out.

My understanding is that weapons are declared for each round rather than each action.