Berlin in February help

"...a great deal of walking.?" You can go from Alexanderplatz to Nikolaiviertel, to the Lustgarten, (you see the 3 statues of commanders, Scharnhorst, Bülow and Blücher), Bebelplatz, then over to Unter den Linden, then all the way to Brandenburg Gate, past university, Neue Wache, Reiterdenkmal of Frederick the Great, cross over to see the famous Hotel Adlon, then to Pariser Platz and the Gate itself and see it from the western side, Vormärz

I didn't list them all in the order as you go from Alexanderplatz to the Brandenburg Gate, you'll see them all if you track them carefully

Or, take a more circuitous route to reach Museum Island, then down to Bahnhof Friedrichstrasse, get to the Brandenburg Gate on Georgenstraße. I've walked all over this area, don't know the streets exactly , only know how to get from A to B by recognising "landmarks" and certain streets.

Join some themed walking tours, Cold War, 3rd Reich, Jewish Berlin, Berlin Underground, Alternative Berlin, etc. I like Insider Tours. https://www.insidertour.com/
Perhaps do a side trip to Sachsenhausen Concentration Camp or to Ravensbruck Concentration Camp.

I was in Berlin the last week of April last year. You can walk from Alexanderplatz pass the museum island all the way to Brandenburg Gate and then to the Reichstag (that is the building where the top was blown off during WW2) and they put a new modern glass one. Or to the Tiergarten park (there are all kinds memorials around there). There are all kinds currywurst beer stands to stop coming and going. If you book the hotel just ask them what the breakfast consists of. I stayed in the Hampton Inn before in Nuremburg and remember hard boiled eggs cold cuts cereal fruit stuff like that, hardly a continental breakfast which is usually coffee and some kid of bread or pastry.

You can follow day 1 of this 3-day itinerary from VisitBerlin:
https://www.visitberlin.de/en/3-days-berlin

You're staying pretty centrally in Berlin so there is a lot to walk to, as others have described in more detail. That said, Berlin is huge so the options for side trips are endless. It's hard to recommend any without knowing your group and what your interests are, however. You're walking distance from several of Europe's best museums and a lot of history, but it's good to think of Berlin neighborhoods as a serious of linked "villages" all with something distinct to offer.

It's unlikely any hotel will provide an American breakfast and if they do please let me know because I'd be on that like white on rice. Most likely it will be a selection of cold cuts, cheese, bread and rolls, yogurt, museli and cereal, and assorted fruits, veggies, and condiments. Half-boiled eggs are common, less common are steamer trays full of powdered scrambled eggs and Nuremberger sausages but sometimes for hotels catering to a more American/British clientele.

thank you for the information. I am sure we will have a lot to do

so back to the side trips:
we are interested in history and not really into museums and such. is Potsdam worthwhile?
Would there be something else that you would suggest
Thank you

I really loved touring the palaces at Potsdam. In February you wouldn't have the gardens, but the interiors are really impressive too. The New Palace had an especially unique interior, I thought. It is kind of a lighter site to break up the heavy history you see in Berlin.