Sober Lark,
Yep they are all trained and qualified in three ENG continuation, and well supported by a despatch team (also trained) and Engineering team (in real time and also trained). The companies OPs Manual addresses the when/what and how it can and can not be done (approved of course by overseeing authority). Its all well thought out and planned for as the aircraft is designed to be able to do it.
And as a PAX it is all about the Lie flat bed, cocktails and showers (you wont find that on the twin), as they not qualified for anything else. Nor should they be.