I would be really upset.
They are old enough to be told that their behaviour is unacceptable and that it is your holiday too.
Most kids (and adults) would dream of having a holiday in Florida or just a holiday and it’s something that the majority can never afford.
They are being spoilt and do not recognise their privilege.
That being said, if they’re out on sun loungers on their phones then I don’t see the issue - most people lie there doing nothing or reading a book. So it’s no different.
I would also compromise and give them down time and later starts - when you read them the riot act say this too.
If it’s a paid activity that starts at a certain time, then they need to be up and ready for it. No one stays back.
Sell it as a photo shoot opportunity that they can post on SM too.
If it’s something that can be shifted, then start and finish later to suit their body clocks.
On down days, they do not need to be in the pool if they don’t want to be.
If you are naturally up early, then perhaps use that time to go swimming with the youngest and have some you time. You could also think about meal prepping and so it’s just a case of them warming their dinner up in the evening.
I would tell them to sort their outfits etc the night before and give them 20mins to get ready in the morning.
Give them a time that you will all leave by, then it’s up to them to decide whether they want to get up earlier to have more time getting ready.
They are being spoilt, however they do not understand how privileged they are and perhaps that’s down to you and DH and you cannot blame them fully.
You also need to remember that this is a tough age where they’re insecure, tired and sensitive. And it’s nothing personal to you.