A con artist does one more scam before he retires exposes dark secrets in his family well after his father dies unexpectedly.

1) It’s not a scam.
2) He’s been a con artist even before he died. He also pay for his funeral costs which he didn’t want to.
3) He and his siblings was abused by his father and deserve to be believed.
4) He was told not to tell anyone.

Hi IvyEight6,
This is how I see it (using your own version of logline):

After his father's unexpected death, a con artist decides to pull one last scam by exposing his family's dark secrets.

However, there are confusing points you'll have to address.
Questions:
1- How exposing his family's dark secrets is a scam?
2- Why does he have to do his scam after his father dies? What is the relation between his father's death with his scam decision?
3- What is he achieving by exposing his family's dark secrets?
4- Was/Is anything stopping him from doing so?

You need to address all the above questions. Read your logline from the reader's POV.
Re-write and we will see again.

I hope this helps.