I can see you have been on many more cruises then I have so I'll try to help but will probabaly borrow your thread and ask some suggestions too. I have 2 teenage boys-I know it can be a bit easier for boys then girls. Boys-I can get the to re-wear shorts- I'm pretty sure it might be tough with girls!!
One reason when we go as a family-we do not do formal nights. First off-my boys will no way wear a suit!!
One pair of dockers and a different shirt to change it up is the best I can get out of them coming as close to smart casual as I can. Packing formal for a family of 4 could be alot of luggage including formal wear I'm thinking.
We also share one room so my boys know space is limited. So-I guess it depends on boys or girls and how many rooms. The seasoned Mom cruisers can probably help both of us here!!
Although-this time I saved my pennies and got a Grande suite. So, Moms-will I have enough space for us all?