I haven't commented before though I have followed this thread and the case with some interest. I think the lawsuit is totally frivolous. The grandfather, who is not a doddering old fool, did something foolish. The family is grief stricken and rather than place the blame where it lies is going after the cruise line because accepting the truth is not easy.
I rewatched the video of the incident. The grandfather put his head out that window, and had to lean forward to do so. and his upper body disappears from view. After this he picked the little girl up and put her out the window. After 10 seconds he appears to shift her position. 25 seconds later he falls to the floor and people react. If I were on a jury, and I have been on several, I would find the blame lies with the grandfather alone just based on the grainy version of the video.
I do have sympathy for the family but they need to accept the facts and move on.