Have you already booked your flights?
If not, I'd say: Skip Istanbul and Kayseri, plus possibly Budapest. They may be well worth seeing, but save those for another trip. Starting in Prague will save you thousands of kilometers and give you a lot of leeway in your time schedule.
Some other parts of your route you might want to reconsider are the following:
- Prague - Krakow - Berlin: Just have a look at Google Maps where Krakow is located, and see for yourself if that route makes sense.
- Amsterdam - Belgium - Paris: You will be spending all your time on the road/ railway with only three days for each of those. The time you will need to get to these places is completely disproportionate to the time you will have at each of them.
- Family - Iceland - Family: Unless your family is located in Iceland, that does seem a bit of a stretch. No question about it, Iceland must be an absolutely beautiful place to visit, but does it all have to be on this one trip? Also, please do have a look at the weather conditions in Iceland at that time of year.
Why don't you tell us what you are interested in (museums, culture, shopping, nature, history...). That would make it a lot easier to help suggest what to leave out or what to focus on.
Knowing whereabouts your family is located would also help understand which parts of Europe are going to be essential to you, and which other parts might sensibly be combined to an itinerary with that.
Another thing to consider is that while going by plane may seem like a short trip, it is not just the pure time in the air. You will have to get to the airport in the first place; many airports are not located anywhere near the city. With security precautions at the level they are right now, you will have to be there quite early (recommendations for my most recent inter-Europe flight was two hours). Then, there may be delays. And when you arrive, you will have to retrieve your baggage, which may easily take another hour.
I think you get the idea. Add at least three hours to the pure flying time, and that may give you a more realistic estimate of your traveling time by plane.