Re: my wife, daughter and friend and myself want to take a Cruise....any ideas??
I've done a couple of cruises in the Caribbean. One with Carnival (western Caribbean) and one with Princess (eastern Caribbean).
As for your questions:
1. Get separate rooms. Although I've not been in a large cabin, in general the cabins are small. Get a balcony room if someone is a bit claustrophobic.
2. Kids should be safe if they are sensible and stick together. The boats are large with several thousands of people on them. Like a large shopping mall that no one can leave.
Whether they can find stuff to do depends on what they like and the activities available on each boat. It varies. (I'm not a kid, I got bored). A lot of the traveling is at night, so if you take a cruise without a lot of "sea days", you get to spend more time on the shore trips.
3. You will spend more money than you budgeted. The lines lure you in with a low cruise charge and then come the land excursions, miscellaneous fees and "tip" charges. But by all means, do the land excursions and don't stick around the boat. It will add up in the end, so be prepared.
4. Take formal clothes. Some lines actually require them for the main dining room. Dinners are usually very good there. That said, try not to eat too much. You can put on 5 pounds or more on a one week cruise because the food is abundant and usually everything is included.
5. There is no such thing as a good casino. That said, your girls might be able to sneak in if they look a little older and they'll get a kick out of that (though you may not).
6. Nights are pretty good. The Carnival cruise had a Karaoke bar where we hung out most nights, but the one on the Princess was bad and only at certain times. Most boats have separate dancing places for adults and teens. Not sure about all night, though, most entertainment (except casino, IIRC) ends at some point.
7. I was bored when the boat was at sea during the daytime. People do the pool and drinks, which I don't get into. Or you can eat...all day long. Sea days suck.
8. You probably won't get seasick unless you hit a storm. Try to avoid peak hurricane season in the Caribbean (late August through September). You will take some time to regain your shore legs once off the boat.
Personally, I liked the Carnival Cruise much better. The call them the "Fun Ships" and it was more fun, and also more informal. The Princess boat was more elegant and the food was somewhat better, but the activities were lacking.
One thing you may not thought about is old people. A lot of old people. The ads show families and young couples, but there are a lot of old people on cruises.
I'd cruise again, but I'm not a big fan. My family is kind of split on the issue, one daughter and I are meh, while wife and other daughter are ready to go again.