Hi @Jero Cheng,
Thank you for posting to Microsoft Community.
Based on your description, I understand you want Ken could receive two emails even though he is a member of group in To box.
I'm afraid there is no such setting that allows ken to receive two identical emails since ken is duplicate in To.
However, after a few tests, I suggest you could create an inbox rule to work around the issue as screenshot below shows.
If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.