Within the context of the company, it's his responsibility as an founder and an executive. His wife (AFAIK) has no formal title or role at the company - all her power and influence is derived from his status as a founder/executive.
Yes, as a person with free will, his wife is ultimately responsible and "shouldn't" have done what she is alleged to have done. But in the context of corporate governance and law, he is responsible for allowing her to have privileges and access to the company that are quite unconventional.
If the wife has a formal, executive role at the company, then that's a completely different matter. I'm just speculating based on the usual way of things - I could be completely wrong.
Yes, as a person with free will, his wife is ultimately responsible and "shouldn't" have done what she is alleged to have done. But in the context of corporate governance and law, he is responsible for allowing her to have privileges and access to the company that are quite unconventional.