PerverseConverse, well I don't know what they're thinking at the moment, because we haven't discussed it.
The things that people here have made me think about are that the baby might not be so happy to be left when she's five months old (she might refuse a bottle, start teething, develop separation anxiety), and that her mother might suffer more than she thinks with engorgement. Tbh, I hadn't given that part of it much thought, because she finds it so easy to express, but what if the breast isn't fully emptied, etc?
So, those are the things that I would mention to her, if it comes up in conversation. They might have already considered them, of course.
I think they are unlikely to discuss it with me, though, now, because when she told me at first, (in spite of what I've said earlier on this thread) I was surprised and concerned, and although I didn't say anything, she will have picked up on that.
The parents are not selfish people, they both put the baby first in everything. But maybe they need this time away, time as a couple. It's not easy for them, us all living on top of each other.
I just wish they would go somewhere in the UK, and for one night, instead of two.