I agree dress up and enjoy i.
On NCL despite Formal being optional - we find that 75% of peopel will get dressed up. Especialy as yours is a New Year cruise then perhaps even more will. DH always takes a suit -not a black tie - and I stock up on those floaty dresses from Per Una [M&S] and some smart silk evening trousers and a selection of tops. Should be lovely and hot for you.
We've cruised with NCL a couple of times. The thing to remember about the formal night is it gives you chance to really dress up. There are quite a lot of men in Tuxedos as well as suits/jackets, however the ladies always seem to wear their finest. Nobody is frowned on for wearing a suit or jacket - some people have travelled long distances by air with limited luggage allowances, also a lot of people don't have a tuxedo these days anyway. My wife and I always 'go for it' because we have less opportunities in our social life for black tie events, and enjoy the chance on a cruise. There is something about walking on deck after dinner dressed in a tuxedo with your partner in a cocktail dress that just can't be put into words.
Just do whatever makes you comfortable and happy.
Cruised on NCL Dawn at Easter around the Caribbean with our 2 daughters aged 13 and 14. Tell your wife and daughters to pack all their dresses and they can dress up every night if they wish, as the restaurants are all lovely and you can be as formal or informal as you wish. Have been on several Caribbean cruises at Christmas and the weather is generally around 30 degrees. You'll love it.
We have been with NCL to the caribbean at Easter time and loved them for the freestyle dining, we will definately cruise with them again. They are not as formal as some cruise lines , however a lot of people do get dressed for the evenings, my husband takes a dark suit ( he does this for all the cruises we go on, and even on the formal ships he is not frowned upon or out of place for not having a tuxedo, lots of other gentleman do not wear tuxedos ) I do not wear a long dress when we go on American cruise ships as not many Americans seem to wear long dresses, I do take a couple of sparkly cocktail dresses with me and also ,as per a previous writer, have some of the per una dresses and tops. However as this is a Christmas cruise perhaps more ladies will wear long dresses. You will have a fantastic time and it will probably get you hooked on cruising, make sure you see the acrobatic show they do, it is amazing.
If your wife does not want to spend too much on evening clothes for herself and your daughters it is worth going to TK Max, I have had some lovely evening dresses from there for myself and my daughter at a fraction of the cost of Debenhams .To help with the luggage allowance, because you do not dine in the same place or on the same table every night no one notices if you wear the same outfit/dress twice, after all you only have it on for a couple of hours each evening. Take a look at cruisecritic.com it is a cruise chat room and has tons of information on it, if you register with them ( no charge for this )you will be able to access all areas of the site and can go to an area titled roll calls, this is where other people on the same cruise as you chat to each other. I did this for our cruise and as most of the people had cruised with NCL lots of times I got a lot of really helpful advice from them and we all then met up on the cruise, it was really nice to meet the people who had answered all of my questions.
Hi, I have just returned from cruising the southern Caribbean on the Norwegian Pearl. Regarding the luggage allowance. What makes you think that you only have 20k allowance. Usually the flights are with scheduled airlines such as AA, BA or similar and the allowance is 2 x 23k per person plus 1 carry on at 18k you should double check with your agent which airline you are going with. We took formal wear and one evening we were certainly the odd ones out but we didn't care, I should think that people are more likely to dress up as it is Xmas. Because of the freestyle dining you are unlikey to be seated with the same people so just taking limited evening wear should not be a problem. There were plenty of free laundry facilities(apart from soap pdr) We enjoyed the cruise, a little disappointed with the food, it was often cold in the buffet. A warning, apart from the buffet, the restaurants operate a reservation system and unless you call at 7am which is when it opens you are unlikey to get the time you want. As you have fairly young children I would suggest 5.30 - 6pm then you can catch the early show which usually starts at 7.30. The main restaurant was the Summer Palace and is lovely but half the time it was empty, strange! Would recommend Mambos (mexican) it was really good. We were annoyed as after trying for several days to book the Italian La Cucina, we arrived at 5.30 and almost half of the tables were still empty at 7.20. The weather was good, it was the week before the storm 'Noel' fortunately, a few showers which you would expect this time of year. The ship seems to cater well for children, there were kids clubs for different ages. I am sure you will have a wonderful time.
We are also going on the same cruise as you and we are planning to take at least one formal outfit (for New Years Eve ) As someone else suggested take a look at the cruise critic web site where you will get a lot of information. Enjoy your cruise we may even bump into you there.