Well, UIButtons cannot be triggered in VAM by anything else than a click on them.
But there are ways to bypass that.
Without any additional plugin, you can add other atoms that use triggers and which can be externally triggered, such as UIToggle or AnimationPatterns.
For instance, put all the desired actions in the Trigger tab of your UIToggle. Then add a trigger in UIButtons A & B that'll trigger your UIToggle. Just be wary of the fact that some actions will be reversed when untoggled; that can be avoided by triggering it twice.
With AnimationPatterns, do a very simple non-looping 2 steps animations with triggers in it. Use the "ResetAndPlay" trigger to start it from a UIButton.
Or you can use a plugin. "Relay" from
MacGruber's LogicBricks does just that.
It's the same idea: you put your trigger actions into any atom thanks to the plugin and then add only 1 trigger in your UIButtons that'll trigger it.