Building without work plans

You will be involved with the garage insofar as you will be building the foundation for it

What do you think about simply putting a stop here?
It makes little sense for us to publicly argue back and forth here, especially since the matters are already in the hands of the lawyers. Wouldn't it be more sensible if you just waited to see how things develop? Now let the lawyers handle the legal matters.

I consider quoting an email taken out of context to be dishonest

Dishonest? I would rather say that applies to you. The only thing missing from the quote of the email is: Attached you will find the order form for the garage with the request for signature. Best regards Thus, it is not taken out of context.

I had confirmed that we had overlooked, as laypeople that we are, that the plans written by your architect did not correspond to our wishes and agreements. We could not assign the height specifications. Therefore, we needed another consultation, and you denied us that, or rather, it would have been charged to us extra. Your architectural service looks like this: the architect comes to the client for 2 1/2 hours, and then everything is discussed. I don’t know anyone who has experienced anything like that. That we wanted the house to be higher, I can confirm based on an email to Mr. B. from the Massivhaus-Zentrum. Please also don’t keep saying that the planning was fine. After all, part of the finished floor would have been 20 cm below the ground. Maybe your house looks like that. I’ve never seen anything like it anyway.

Today I received an email from Mr. T., in which he writes:
"Due to the short-term transmission of changes, it is not possible to start the masonry work on the ground floor on 01.08.16."
I had already informed him on 8.7.2016 that the plans were faulty. However, he saw no need for the architect to finally sit down with us and discuss the plans.

Let the lawyers clarify the legal matters now.

That's exactly what we are doing.