Hi @yinyin, I want to add my welcome and to check in. I think you might find this blog article helpful written by Mayo MCI expert Dr. Chandler:
- Is it Denial or Something Else? https://connect.mayoclinic.org/blog/living-with-mild-cognitive-impairment-mci/newsfeed-post/is-it-denial-or-something-else/

Excerpt
"this "refusal" to admit to memory loss or inability to see it isn't defensiveness at all. A person with MCI or dementia often has another change in ability - the ability to see themselves clearly."

Sometimes it can help to have someone else be involved like a social worker perhaps? Would it help if you asked him to explain certain aspects of the family finances to you - one step at a time? How are you doing?