For the boys I have to recommend the jeep safari, but be prepared to get wet and dirty, its a fantastic day out and they will have a blast.
There is also quad biking and go carting not far from Icmeler.
There are the normal boat trips which can be either lazy day or you can get the full party atmosphere boat.
Two great water parks in
Marmaris which can be a great day out.
I can't think where the Hidden Valley apartments are but it says on the website 1200 metres from the beach so I imagine you will be 10 minutes walk for lots of restaurants, 15-20 minutes walk to the centre.
The boys are old enough to do a few things on their own together so you may get a quiet break every now and then.
Have a great holiday and please let us know what you thought on your return.
Dave