Too Much for one trip?

IMHO, way too much to see in that period of time. You have to figure at least half a days travel between places. Are you only spending one night in each place? That would only give you half a day's sightseeing. Some of those places (London, Rome, Paris) should be at least two full days (3 nights) and even then you will not see much of those. I would eliminate some of these places and plan on going again some day.

Yes, you are right. It's too much. You are having less than two days for each location not even counting transport time between locations. Consider allocating at least four days for each location (including transportation). That will leave you five locations for your twenty days.

Too much. Even if all those destinations were grouped tighter together, it would be too much. But even worse, they're scattered over diverse regions of three of the biggest countries in western Europe. I'll let others make more detailed recommendations on how to slim this down, but here's my two small pointers. If you want to visit the Alps, give yourself at least three nights, meaning two whole days. This is a very "weather dependent" region, and the volatility of the storms can scuttle your plans if you don't build in some flexibility. Three nights reduces the chances that those wonderful mountain views will be hidden behind rain and fog for the duration of your visit. Also... the Berner Oberland is only one of hundreds of worthwhile places to see the Alps. It is one of the more impressive, but it's a far outlier for your proposed itinerary. Except for the extreme southwest corner, you can't get to Italy from the rest of the continent without passing through the Alps. So, if Italy stays on your trip, I would recommend getting your Alpine thrills as you pass into or out of the country.

As the others have said, way too much in the time you have allotted. You need to trim the number of places you go and/or increase the time you have. I have family in Hannover and Cologne, but have never been to those places. But I have visited with them. On two different trips they have met me, once in the Black Forest (for a family reunion) and once in Bavaria. Can the family meet you in Munich or somewhere else? I suggest you and your travel companions get out a map of Europe and see the distance between places. You have to be realistic about what you can really do. Italy was on the top of my list for countries to visit, but I didn't get there until my 4th trip. Just remember that you can return some day. To utilize your time, fly open jaw, into one city and out of another. Look for multi-city when you are looking at airfares.

You have listed enough places for several. Italy should be 1 (or more). England another. France one. Germany yet another. With 20 days, you could do a sampler of 'the big 3'- Paris, Rome, and London. Or pick 1 major area (like Italy) and plan 2-4 bases with a few day trips from some. You need to talk and research some more. Then work out a good way to prioritize and try to have something in the trip for each of you.

Thank you so much for all your comments I knew it would be too much but didn't want to admit it do it is good hearing it from others. I will consider asking family to meet in Munich that is a great plan!! I think we will be extending our time so we can spend more time in places as well. I defintly want to do London Paris and Rome so I will have to consider which 'countryside' locations would be best to visit.