Looking for a base city in Bavaria

Garmisch-Partenkirchen or Berchtesgaden might be suggestions for you. They may be smaller than you might want, but are both in beautiful locations in Bavaria. Both are accessible by rail.

The problem is travel time to and from each place. Munich is the obvious choice of a base, for day trips to either Nuremberg or Füssen (Neuschwanstein). GP is relatively handy to Munich or Füssen, but would be about a 3 hour train trip (each way) to Nuremberg.

When is your planned trip, and what sites have you used to search for accommodations? I took a very superficial look at booking.com and vrbo and found quite a few possibilities in Munich. Your options would increase exponentially if you looked at 2 apartments in the same building.

You will probably need 2-3 apartments. How many days ? Bavaria is quite large with places to see at the far north and far south of the state. Consider 2 locations

I agree that you should look for two apartments in the Munich period. Munich is really ideally suited for day trips, although it would help to know what day trips you have planned besides Nuremberg. Nuremberg actually would make a decent base but that's only if you're not heading into Salzburg or Füssen and places like that. If you're going both north and south, then definitely Munich would be the best place to stay.

Look at Booking.com like others have suggested. They have a strong set of filters you can use. And I do think that getting two apartments would be best. There are plenty of places that have apartments next to each other .

Now we are looking at possibly Ausburg, but are there other cities to
consider? We’d love a charming, old world town with good rail
connections.

Augsburg is charming, but it is still a city and fairly modern in places. And while it has good connections, it's still a long way to other places you plan to see (Nuremberg, Neuschwanstein...)

I will happily nominate the town of Bad Windsheim for your consideration.

"Bad" indicates a spa facility. There's a nice one in Bad Windsheim. But there's more to this small, old world town - including a fascinating outdoor museum - the Franconian Freilandmuseum, where dozens of historic buildings from the region have been relocated so that visitors can experience a bit of what life was like here over the past 6-700 years.

https://www.tripadvisor.com/Attraction_Review-g198421-d284746-Reviews-Frankonian_Open_Air_Museum-Bad_Windsheim_Middle_Franconia_Franconia_Bavaria.html

Bad Windsheim is a SMALL old town with many intact half-timbered buildings, mostly FLAT town that should be simple to negotiate on foot. Aerial view of BW: https://www.nuernbergluftbild.de/images/luftbild/Q09120064.JPG

And it has good connections to Nuremberg as well as to Rothenburg ob der Tauber; both are less than one hour from BW by train. If you wish to explore other nearby old-world towns, Iphofen, Ochsenfurt and Marktbreit, sister-towns on the Main River, are also less than an hour by train. Würzburg is just a little over one hour away.

The town of BW has several nice restaurants as well:
https://www.tripadvisor.com/Restaurants-g198421-Bad_Windsheim_Middle_Franconia_Franconia_Bavaria.html

I too had my first visit to Nuremberg roughly 50 years ago. It too has an exceedingly charming old-town zone that is largely walkable - much of it is pedestrians-only, in fact. It could make for a good base town too, though I would not call it a small town with 500,000 inhabitants.

The big outlier is Neuschwanstein. It's 5 hours round trip to the final castle bus stop from Munich. That is not a good day trip as far as I'm concerned. So if you are determined to go there for the half-hour tour, then you really should just travel there by train and stay there a night or two. See Füssen and the area, make the trip worth your time.

Back to your accommodations... In Bad Windsheim, there's a reasonably priced place right in the heart of town which rents apartments called FeWo Nebenan. I just checked a random week in May... 7 nights, 9 adults (just in case you forgot someone) at booking.com... results show two apartments - a ground-floor apt. for 3 and another apt. for 6, total price for the week = US$1649. Reveiws are very positive.

I would spend a final night or two in Munich - if you decide to drop Neuschwanstein Palace, which would be my recommendation, then you should visit Nymphenburg Palace in Munich. It's a fantastic place with lots to see.

https://www.theworldisabook.com/16991/munich-with-kids-nymphenburg-palace/

We lived in Augsburg for four years and loved that ancient city. It only 30 minutes by train from Munich. Also, it is on the Romantic Road and you can go north to Rothenburg ob der Tauber or south to Fussen and Garmisch.

I agree with other that you are better off looking at booking 2 apartments (search for Ferienwohnung) as finding something big enough for 8 people with 2 bathrooms will be very limiting. I typically book using booking.com in Bavaria (you can limit the seracht o just apartments and homes if that is your preference).

Munich is where I would base out of, specifically near the Ostbahnhof or Rosenheimer Platz area for easy S-bahn and train connections and to avoid the construction near the Hauptbahnhof.

If mobility is an issue I would suggest just getting 4 rooms in a Motel One. It is a Munich based hotel chain with modest rooms but really excellent lounges made for hanging out. Accessibility can be an issue with apartment rentals. Motel One is my go to when I'm taking groups of people to Oktoberfest.

DJ

Why not stay between Munich and Nuremberg? Ingolstadt is perfect for visiting either, and there's stuff to do around that city also. I'm going there for a four day weekend in two weeks, with plans to visit the Audi Museum, the Jurrasic Paleontology Museum in nearby Eichstatt, and the Schloss Neuburg an der Donau.

Take a look at this place, I think they could accommodate you. https://schloss-sinning.de/