We have traveled on msc cruises four times and whilst we could not be sure of the tempreture in the pool it should be ok.the dress nowadays is not that formal and a shirt and trousers should suit if tidy.
I was on MSC Musica last year and the pool - like most, are not heated. Formal evenings were very mixed. I even saw people coming in in their overcoats! Just aim for the middle ground. Children were everywhere - Italian ship, so informal style. Midnight I saw children as young as three scampering around in the main lounges. Very easy going ships. Audrey Osterlyng, Brussel.