How would you approach a deeply delusional friend/family member?

I have a family member who has lived the last few years of his life in essentially a fantasy land. No drugs or alcohol, all of the problems are just due to a severe case of living outside of reality. He’s probably slightly below average intelligence but he’s not an idiot and doesn’t have any special needs.

The delusion boils down to him essentially working a low skilled position for a huge company and representing himself as very high up. I don’t mean he lies on his resume which wouldn’t bother me I mean every time he talks to those around him he talks about these massive projects he’s working on that one of the ten biggest companies worldwide would not be entrusting to someone without a college degree. He posts online about his great exploits including meeting with Senate leaders in Washington DC to negotiate land deals for the company (I’m telling you there is a 0% chance this is true).

Lately he’s considering a run for office since apparently he had a debate with several popular House and Senate leaders recently and they told him how great all his ideas are.

He’s approaching 30 years old and lives in complete fantasy, either he is so immature that he thinks adults will buy into his outrageous lies or he genuinely believes them himself. I can list a ton of his heroic exploits but I don’t want to go into too many specifics (one involves assisting in taking down an armed man at work, conveniently did not make the news).

He has one brother who calls him on his bullshit and he hates him. His other siblings and mother at best humor him and at worst enable him. Part of me thinks I should leave it be and the other part thinks I need to do something before his company fires him for lying about his position and duties and he goes further into delusion.