I think a cruise is THE perfect vacation for a mother. Mothers are always the ones who have to plan any other type of vacation- where will we eat? How much will it costs? How long does it take to get there? What attractions will amuse the kids? Etc etc etc. On a cruise it is all taken care of for you.
I recently returned from a May 3 Eastern Cruise with three teens- ages 13, 15 and 17. The 17 YO loved the Common Grounds programs- they had activities from noon until 1 AM- some of them taking all day and happening all over the ship! The teens can get as involved as they want in the programs.
The 15 YO DS did not attend any of the scheduled activities. He spent the cruise playing basketball up top and ordering room service! He thought this was just the best thing! Room service is free except for your tip.
DD 13 was another matter. She hated the Common Grounds program which is tailored for 13- 17 year old kids. I thought she was going to love hanging with the older kids but no way!! After two days I begged them to put her into the 12 year olds programs- they had a lot more structure to thier activities schedules and a lot of variety. She was happy here. I think what happened is that she is a leader (read bossy on her bad days!) and there is no way a 17 YO is going to be led by a 13 YO- so she felt intimidated. In the younger group she was able to shine!
Although Dis does not advertise it there is a certain amount of flexibility in the age groupings. I would advise registering both girls for both programs since they are both on the cusp of the age groups. This way they can pick and choose what they want to do. Be aware that DD13 said that a lot of flirting and "pairing up" happened in the Common Grounds area. Harmless I am sure but she felt uncomfortable with it.
So take the cruise- you'll love it!
I have tons of budget ideas if you want them- e mail me and I will share them!