don't let cruising with kids overwhelm you. your 16 yo will be just fine on his/her own. just make sure to set check in times with you, eating times and night time curfew! as for the the 8 and 5 yo (16 yo also if it'd make you feel better), take advantage of the on board kid camps and services. they will have a blast and you can relax and rest assure they are well taken care of. take the kids to lunch, bring them to the pool for some fun & sun and maybe take them back to camp so you can grab a nab or some spa treatment.
on the ports, make sure and let the kids have an opinion on what excursion to go on. it will make it more fun for everyone. if you decide to just tour and shop, be careful cause the shop owners know how to rangle the kids in to pressure to into buying things you don't want. just stand your ground and let the kids know the ground rules or spending allowing before hand!
that's all for know, happy planning!!!