The Reason Hilda, Frida and David are with the Crew is because They were killed by Arthur in Matticraft's Body.

Hilda was exploring with her friends, and suddenly, Arthur pushes her into a chasm, she gets impaled by a stalagmite, her heart and veins at the tip of the stalagmite, and her eyeball also impaled by an stalagmite.

Frida got her legs biten off by Arthur, the blood loss killed her.

David got half his head bitten off, and lost his insides.

Matticraft was lucky to regain control, but looking at the damage done... he felt a remorse... Johanna and Anders saw everything, and asked Matticraft to help, Matticraft, Kai and Xenocraft gathered and decided to use their genomes, and revive them, Xenocraft, used his organs for David (don't worry, Xenocraft regenerates them), Kai uses Lethalnium for Frida's Legs, and Matticraft... He bites Hilda in the stomach, Injecting the Genomes and Toxins from his DNA, Hilda started shining, as radiant as the sun, and her body grew up as large as Matticraft, as she woke up, she looked around her and saw David and Frida dead, she started crying, Xenocraft injects his venom (media his tail) to David's Chest, David glows like a Red Sun, and then he wakes, Frida woke up from the Lethalnium overtaking her, but Kai injected his venom in time, Frida gained her control again.

In other words, The trio was revived.