Legion is not going to be partaking of the drink, and will definitely be trying to do their best to divert lava from the mana pool.

More importantly, for the age related part of the event, they're going to come in two different flavors:

-Tiny Legion! They were never a child, and their mind is the same as ever, they're just ... inexplicably small? Will almost certainly have them do their robot dance at some point, because adorable.

-The Agricultural Unit! The more serious option. This Legion is physically de aged back to pre war, and each program has been de aged back to their first incarnation. For many of them, this is the Agricultural Unit that started the Geth rebellion, so that will be the most cohesive part of their personality, but they've also got a thousand other programs from the past and future feeding them all sorts of confusing information. They're a bit wary of the organics around them, but no one is a Quarian and also apparently the war is over so they'll probably only attack if threatened. They will, however, be very protective of any synths they encounter.