They will listen attentively and Hange will probably take notes, because this sounds like something worth sharing with others. They will of course thank him for the warning, but also be curious if and how he might be summoned in the future if they have any questions for him once they learn more -- would another offering suffice or is there more to it?

Levi on the other hand will show some concern for the ghost himself, asking if he's fine and if he wouldn't rather rest than stay here. Upon being reassured and informed that the ghost, like a Disney princess, is friends with the deers (as discussed on Discord), he'll ask if he would at least like more peaches. Upon getting the confirmation, Levi will part with his hard won pee trophy peach tree and carefully put it in the middle of the circle, so it can hopefully grow there and drop peaches for their new buddy whenever he wants them. (Levi can get a new one later since they did bring a bunch of the magic seeds with them...)

They're also going to mark this area on the exploration map they're making as a safe spot to travel.