Just returned from a short stay (2 nights) at Vero. It was our first time and I thought I'd just put down the following thoughts that may help you.
Our group was 4 adults, and 3 boys, 1-13, and 2 ten year olds. our trip was combined with other visiting in Florida so we had rental cars and flew out of Orlando.
The pool is great, the kids loved the slide. The hot tub gets crowded fast. The mini golf near the pool is fun, but not that elaborate or challenging (didn't compare to the WDW courses, but being Disney, better than most resort areas).
There is a ping pong table (1), shuffleboard (1), basketball hoop (half court - 1), tennis courts (2). There's a croquet lawn where activities such as croquet, lawn bowling etc. go on. We saw many times the teens had pick up football games going on there, frisbee, nurf ball etc. (they provide lots of balls etc at the Eb and Flo's rental area).
There are lists of daily acitivies that are mostly geared toward the younger kids. Our 10 year olds were on the cusp of the interest scale there. Again being boys the crafts etc. didn't draw them in. I did see teen girls doing more of the crafts etc. though.
There are bikes to rent, along with the beach items mentioned by scootert above. There is a tennis pro available for lessons, they did have organized teen dodgeball and that was a huge hit with the kids. Must have been 40 kids participating in that event. There's also an arcade (small). They have sing along camp fires and make smores. We participated in a star gazing activity that was amazing -beautiful clear sky and without a lot of ambient light just magnificent views.
We were there this past week and even with the Christmas/New Years holidays it didn't seem that crowded. However the "fancier" restaurant books up quickly and Shutters, the other on site restaurant was great for us. Good food at all meals and we were able to get a table without problem (July may be a different story here as well).
There is a counter service/bar by the pool but the service when we were there was painfully slow and they don't have another option like Roaring Forks at VWL or Beach Club's Marketplace etc. I feel they could really use that.
There are other things to do such as scuba lessons, snokeling, surfing, fishing, kayaking etc. but these are additional fees and some are off property. They may be the types of things to add interest to the older teen.
I would say that yes a car is necessary. For shopping, eating off property, going to local points of interest or some of these other activities (Surfing).
If relaxing and laying on the beach all day is what you are looking for this is the perfect place! If the kids are always on the go and have trouble amusing themselves you may have to get a little creative. 2 nights/3 days for us was perfect. The kids loved being able to go off on their own to many things and make friends with other kids there to do things with.
It's a relativley small place compared with the WDW resorts and that has its good and bad points. I think that July is "in season" and there will probably be a lot more going on.
We had a wonderful time and look forward to going back again. The kids did have their "I'm bored" moments but not one of them was happy to leave and more than once referred to the place as "paradise".
I hope some of these randomly flowing thoughts helps. It will really depend on what your kids are like - especially the 16 year old and how easily they might make friends with other kids to help pass the time they can't relax during. But one thing I think you will want is a car.
Hopefully others who've stayed during the summer months can advise you better.
Enjoy.
I just hope I can handle being in Florida, but not with 
!!!
