Family trip + language course

Loads of sights for two weeks sound like Berlin (incl. Potsdam), Hamburg or Munich.

In terms of accent free High German Berlin is the best choice of this three - even if in the center part you will find a lot of languages spoken.

Tip: let you boys try Babbel app to learn some German before. They can also start reading some news in English and German on www.dw.com.

Thank you MarkK! They have already been studying German as a second language at school for years now. They have passed the A2 FIT exam but we hope they will get better im fluency and conversation. Can you suggest options for areas and accommodation? We would like family house stays or apartment rentals but not too far from transportation.

Why not enroll them in a student exchange program?

Learning another language, or just have some basic phrases are great.
Still, you really won't need it, since many Germans speak English. I enrolled my teen daughter in a six week Spanish immersion course in Mexico (we lived in Arizona) and it really helped her learn the language.

As for where to stay for two weeks, I would go with the following in order of my preference:

1) Munich, allowing you to visit places like Augsburg, the Romantic Road, Fussen/Garmisch, Berchtesgaden/Salzburg, Nuremberg, Regensburg, Passau and more.
2) Berlin, visit Dresden, Potsdam and much explained by previous poster.
3) Rhineland, two areas: First, south, Black Forest, Triberg, Baden Baden, Strasbourg, France, Heidelberg, Colmar, France, Titisee, Friberg. Second, north, Rudesheim, Cologne, Trier, Luxembourg, Mainz, Frankfurt.

Bravo that your boys want to learn German and are pursuing this study.

On learning the language, the more the better. You cannot over learn. The hard thing is which method(s) to use to bring about the most language acquisition in the time you have.

I don’t know about finding a course, but otherwise I would try to stay in a small inn with an older proprietor. Many of the places i have stayed like this, very little English is spoken. I would forget a larger, tourist town and seek a small town with good transportation links. Last fall we spent a week in Lichtenfels, north of Bamberg. I only recall the tourist office lady speaking English. Others might have been able to speak some, but we only communicated in German.

If your sons had 2 weeks, 24/7, of immersion in a linguistic environment that was completely apart from you (with a German family for example) or in some similar setting, they would have a promising environment for developing their fluency and their conversation skills - and they would surely see some measure of progress from that experience.

I don't think I would waste time or $ on study in night courses and such as they have already been in artificial classroom environments for years.

A "student exchange" program like Tim suggests for a period of months rather than weeks would be the more effective way - a full living environment with work/study, and a social life is the best language class!

But the way I read your posts, you're looking for some family time together. So just go and have a good time. Maybe your boys could take the walking tour (of whatever city you are in) that is offered in German, while you take the English Walking tour. Allow them to take turns handling your restaurant, hotel, tourist-office, and train-ticket interactions, etc.. They will surely pick up a few skills as they do these things. But really, the more important thing for a short stay like yours is to make sure they further develop an interest in both the language AND the culture, that they see/do things that will MOTIVATE them to seek out that culture and acquire more of that language - later on, as temporary residents abroad, at some point in their adult lives. Play to their interests. If they are science-oriented, you could make sure they visit one of Germany's technology museums. Even if they need to use English-language materials/tours to get something out of it, they'll be seeing their area of interest from a German perspective. I think the same is true whatever their interests - historical periods, or art, or sports.

We are open to any location in Germany but of course we want to stay somewhere with loads of interesting sites and activities because we will be staying for two weeks!

This is a list of language schools in Bavaria: https://www.languageinternational.co.uk/german-schools-bayern-1913

I really like Russ's idea of having the boys take local tours conducted in German.

Everyone has been extremely kind and helpful here! The boys have already been to an immersion program for 2 weeks a couple of years ago and it was helpful. I'm afraid the longer option isn't possible at the moment. I like the idea of the tours in German and taking turns in conversation. Maybe we could just do that, skip the lessons and focus on more fun. I'm sure the boys will appreciate that 😁