Many/most people don't sleep well on overnight flights, so the first day in Europe is often very hazy and not very productive. This hits people differently, so don't assume your party will be physically capable or desirous of hanging together on Day 1. Arrive with information about sights in hand but don't count on doing much more than wandering around--preferably outdoors so your body knows what time of day it is. Gardens are good, or perhaps a walking tour that doesn't require pre-booking. If someone slept the night away on the plane, he can take on something challenging--like a museum--that (ideally) interests only him.
I highly recommend stopping by the tourist office (airport may have a branch) to get maps for everyone, the latest opening hours of key sights, and information on current special events or activities that might be of interest. This is how I have discovered walking tours, cooking classes, small festivals, etc. Also unexpected site closures. Check online for the location(s) of the local tourist offices, because they do relocate, and guidebook addresses can be outdated. I spent an hour looking for a T.O. in Berlin and finally found out it had moved from a souvenir-store clerk.
In the absence of a special reason to do otherwise (check museum closing days, etc.), I would start in Munich. Its sights seem less spread out than those in Berlin (not hard to accomplish!) and you're more likely to find a centrally located hotel from which individuals can easily wander in different directions, at least in some cases on foot. Jet-lagged first-timers arriving in Berlin might feel less comfortable going off on their own because the city doesn't feel like an intimate place and they might need to use public transportation to get around.
Day allocation is a very personal thing. I think it's safe to say that the people who love Berlin will say it needs more days than the Munich-lovers will say Munich needs (aside from out-of-town side trips, at least). But I'm not sure that is a very useful guideline, especially when you have a max of 8 days. Still, I'll stick my neck out and say maybe 3 days (including the jet-lag day) in Munich and 4 or 5 in Berlin. If some folks have had enough of the relatively modern surroundings in Berlin by the third day there, they can take a day trip to somewhere like Potsdam.
For the extra time some of you will have, I'll mention three especially pretty cities/towns I enjoyed in 2015. All are in the eastern part of Germany but too far from Munich and Berlin to be day trips.
Quedlinburg: Over 1000 historic buildings, many of them half-timbered. Definitely has been discovered by European tourists, so you would not be the only tourists there. But off the main streets it is not tourist-thronged. There's a castle, a cathedral with a very impressive treasury (Google for the American connection), a modern-art gallery (Feininger), and the tourist office runs a daily English-language walking tour. Alternatively, you can rent an audio guide. The walk takes several hours aside from time at the castle and cathedral.
Görlitz: So many historic buildings (half-timbered with the occasional art nouveau interloper) that it is used as a film set. Sits on the Polish border east of Dresden. Lovely place not quite as polished-for-tourism as Quedlinburg and certainly with fewer tourists due to the obscure location. Interest may have picked up since I visited in 2015 due to The Grand Budapest Hotel, which was partially filmed there.
Erfurt: University city with the usual lively atmosphere. Handsome architecture that survived the war, including the merchants' bridge across the narrow river. Historically-important Weimar is nearby and worthwhile, and Buchenwald concentration camp on the outskirts of Weimar has good explanatory material covering not only the war years but the post-war period when the camp was used for enemies of the communist regime.