Post-alien war story about a young man searching for his younger siblings and some kind of fanatical Doomsday cult planning to end the world

I read this book in my school library a very long time back. Like around 2004 or something like that. Didn’t get to finish the whole book through. But from what I could remember,

• Story takes place in 1999 during the final years of the 20th century.
• The book has an alternate history. It is set in a sort of post-alien war world.
• There are 2 types of humans: evolved humans called E-Humans and the old humans i.e the ones that can’t evolve. Most of the humanity has evolved and old humans make up only about 2% of the whole population.
• Technology has also rapidly evolved as the war ended. But the heyday of that growth and prosperity has long since passed.
• Decadence and complacency have taken over the people along with the decline in the values and morals. The enemy is no longer some kind of vicious creature or an alien entity but is the one that is lurking deep within every humans soul.
• The main character is a young man who lives in an apartment along with his very young sister and brother. Their parents abandoned them. As a result he quit school long time back and works multiple jobs to take care of his younger sister and brother.
• Three months before the start of the story he is diagnosed with cancer and learns that he doesn’t have much time left. Cancer actually has no effect on the evolved humans. But he is unfortunately, unlike his younger sister and brother, an old human / unevolved.
• His life turns even more upside down when one day after coming from work he finds his younger brother and sister missing. And the police do little to almost nothing. He decides to search for his siblings on his own.
• Eventually after digging up and looking around for information for a long time he learns about a Doomsday like cult that have abducted his younger siblings.
• After learning about it I think he immediately rushed into one of the cult’s base underestimating their power and network. He is almost killed, I think, but he is rescued by some old man.
• The old man seems to know about his parents. He was the commander of a special division within the military during the alien war.
• I don’t remember too much after this. But, I think they also find out that the cult is trying to open some kind of portal to the sun that will destroy the earth. And the cult are gathering and/or abducting highly evolved humans to create the portal. The main character and the old man find out that the portal will be complete by January 1st, 2000, 12:00 a.m.