SF novel with a boy and girl who undergo an alien challenge

Question

I'm trying to remember the name of an English-language novel that I read in the late 1990s. It was probably published in the 1990s or the 1980s.

The backstory was complicated (and seemed like it might have made for a better plot than the book's actual main plot). There had been an extensive civilization in orbit around the Earth, but it had been wrecked by some kind of space monster. (I envisioned the monster as insectoid, but I don't know if that was from the book or something I made up.) After the collapse of the sky civilization, there was a lot of violence on the Earth's surface, with "holyfolk" killing people who had too much technology.

The protagonists were two teens, a boy and a girl. The boy was the son of whoever had ultimately killed the space monster. The girl was the daughter of a man who claimed to be the last heir of the dynasty that had ruled the sky civilization. He was reduced to leading a band of nomadic raiders around Africa. When he died, the other nomads killed his second-in-command and abandoned the daughter.

Somehow, the two protagonists end up on a space station operated by a powerful interstellar civilization. Three evil aliens (of three different types; one of them resembles a blood-drinking lamia) arrive with them. While they are there, they all undergo a challenge to prove their worth to the interstellar powers. The humans are placed on a team with a lump-like alien, who goes catatonic for a while, after it sees how unqualified its teammates are. Yet the team somehow finishes the challenge.

I don't remember what their reward was, but the story somehow ended on a positive note.

Answer 1

Mazeway

This is Mazeway, which is the second book in Jack Williamson’s Eldren series, and which is preceded by Lifeburst.

There are anti-technology Holyfolk, who smash the advanced alien knick-knacks:

“One old man. I brought a handful of eldren gadgets, meant to prove what I said.” He coughed and spat on the gravel. “Useless junk! All smashed and burned now, because the Holyfolk took them for works of their demons.” The catch in his voice was almost a sob. “I never—never had a chance.”

As noted in the question, there was also an insectoid entity that destroyed the Earth:

His father tried again to smile. “The eldren called the creature the heatseeker queen. It came out of space and made a nest in an iron asteroid. One of the young came down to wreck the web.”

The protagonists are Roxane Kwan (heir to Kwan Corps) and Benn Dain, who are taken to the titular Mazeway, for the competition known as the Game of Blade and Stone:

Of course Xanadu was just a dream the old poet had dreamed, but Runesong had told him about Mazeway, which was a double world, its two planets named Blade and Stone. He used to wake with those pleasure-domes shining in his mind.

Stone, she told him, was the underground arena for the game. The old Red Delver warlords had invented the rules, she said, when they got tired of killing one another to choose their ruling primarchs, and the caves were still full of their tricks and traps

Answer 2

Prompted by Adamant's comment, I Googled "Lifeburst sequel" and found Mazeway, which is what I was looking for.

From goodreads:

From the depths of space the Seeker had come, to make the Solar system her nest. The invader was defeated, but not before Earth was ravatged, its technology destroyed and its inhabitants reduced to barbarism. Mankind's only chance for salvation lay with the alien Eldren -- but the Eldren considered humanity primitive and savage, and so they witheld their help.

Youn Benn Dain hoped to prove humanity's worth on Mazeway, a planetary doubles whose twin worlds, Blade and Stone, were a testing ground for Eldren young. For Roxane Kwan and Diego BOlivar, Mazeway was a path to control of the dying Earth, and Dain's quest was not part of their plans.

But the Game of Blade and Stone was not designed for humans, and to survive, they would have to work together to fathom the depths of alien minds and the subtle traps of the Eldren way...