There's various ways to do this. As @corerootedxb mentioned, there's rule machine, you could do something with the motion lighting app (if the motion sensors are paired and working with HE), you could use Hue Labs on the bridge, or you can use a free app called iConnect Hue. It's similar outcomes, and the fact that automations on Hue Bridge run local, there's really not much difference no matter which you choose. I run a Hue Bridge myself and one Hue motion sensor (because I refuse to buy any more of those). I control it with iConnect Hue, right on the bridge, so Hubitat doesn't interact with the motion sensor, just the lights it controls. I've tried several times to get my Hue motion sensor to work paired directly with Hubitat. It's such a pain to add it back when it doesn't work, that I've decided I'm done trying. If I ever need more control, I'm simply going to stop using that motion sensor and put in one of the new Samsung SmartThings motion sensors.
Hue triggering Alexa to speak is a bit more challenging. There's Echo Speaks as Bill mentions, or there are also various other ways. If you have the Hue motion sensors paired directly with Hubitat and working properly, then it's easier. Otherwise you'll need to trigger based on the actual light turning on and use restrictions.
Here's yet another way to make Alexa speak. In the post, I also point to a few alternate ways as well.
