Whom do I have to thank in the Acknowledgements section of a Bachelor thesis
The absolutely crucial thing is that you clearly acknowledge and delineate any work, original ideas, results, images, figures, tables, charts, quotations, prose, etc., that were contributed by someone other than the primary author (i.e., you).  Failure to do so could taint your academic reputation, and in extreme cases, might be construed as plagiarism (or some other form of academic misconduct).

Beyond that somber admonition, the remainder of your acknowledgements are a pleasantry which can be doled out entirely as you like.  I agree that extensive acknowledgements in a bachelor's thesis are a bit misplaced.  On the other hand, it's a good opportunity to think about the people who actually made it possible to complete your BS research—e.g., lab techs who helped run and maintain equipment, or administrators in the department who made sure all the paperwork went smoothly.  These people are extremely important and are often overlooked (even in PhD theses).

As for secondary members of your thesis committe, it's up to you.  You can easily say something simple and honest like, "Thanks to Professors X and Y for agreeing to be on my committee."  But I doubt they'll be insulted if you don't acknowledge them for a deep and lasting impact on your research career.  They've signed off on BS theses before.  They know it's no big deal (for them).