jungfraujoch top of europe in august is this possible?

Yes the train runs in August though it's rather a long day trip from Zurich - still possible though.

Just buy tickets at the station on the day - probably cheaper than a tour. It will be expensive - the last few miles up to Jungfraujoch are probably the most expensive train ride in the world. There are various swiss cards that offer free or half price travel on different sections of the route - and will be useful the other days too.

Booking via Viatour seems unnecessary - these are all public trains

http://www.swisstravelsystem.com/index.php may be more useful

Why the hell do you want to book a tour to these places? You can go there easily by public transport. Will be more flexible, more scenic and mostlikely also cheaper (consider the offers of the Swiss Travel System).

SBB timetable
From: Zurich
To: Kleintitlis
To: Pilatus Kulm
To: Jungfraujoch

Go only there, if the weather is fine. In summer, the high peaks are often in clouds in the afternoon. So the earlier you start, the better it is. May be you sleep at Lauterbrunnen and take the first train from there (at 7 am).
You don't need to book anything: the access to all trains between Zurich and Jungfraujoch is free. Just search for the most advantegeous ticket and buy it at any railway station.
Note that Jungfraujoch is at 3500 metres and that some people with heart diseases may have problems at this altitude.