Re: Current HP/Max HP
The new group came explicitly for the reason of escaping the destruction of the world through the Ark. The real question is whether they would know the layout of the ruins for purposes of knowing where to go.
For purposes of this adventure, let's assume they had an advance map and layout and knew basically where to go, just like Leo knew how to adjust the dials on the Time Ark. Or, in another way of thinking, perhaps they had time to explore the abandoned ruins in the future while the destruction of the world was taking place before they finally touched the Time Ark.
Either way, they know the layout, if not all the details of how it all works.