Who wrote the Heidelberg Catechism?
In summary, there is indeed no solid evidence for the longstanding claims that Olevianus was one of two main authors of the HC or that he was responsible for the final German redaction{yellow/}. ... However, the critics have not presented convincing arguments that Olevianus could not have been the final redactor or could not have played a major part in the production of the HC.
Bierma, Lyle D.; Gunnoe, Charles D. Jr.; Maag, Karin; Fields, Paul W. (2005-09-01). An Introduction to the Heidelberg Catechism (Texts and Studies in Reformation and Post-Reformation Thought): Sources, History, and Theology (p. 67).