Children's book about a boy with a benign tumor but then discovered the tumor was his twin absorbed in utero and still haunts him

Question

I'm looking for a children's book series (6 books) each with standalone sci-fi stories, probably published in the 90s (latest early 00's).

The last (or second last) book was about a boy who always had a benign tumor but then started hearing voices, then discovered he had an unborn twin (named Kevin I think) absorbed in utero, effectively becoming the tumor. He enlisted the help of his classmate (Jamie?) to help infiltrate his parents' lab and found they made a synthetic body to transfer Kevin's consciousness into (scratching the surface of the skin on the hand to discover it was made of some synthetic material). He then gets knocked out and when he awakes he hears his parents calling him and Kevin, and his friend looking at him with horror, but his eyesight felt somewhat blurry. The book ends with him feeling some pain at the back of his hand and discovering that he got transferred into the synthetic body instead of Kevin.

My library classified it as a children's book (along with Animorphs and the like) but there were a few more complex words like benign tumor and epithelial.

I don't remember this one as well but the third (?) book was about a series of cloned girls with their names starting with A, B, C, D... etc. The protag (Eve?) found out about the cloned girls with shortened telomeres so they aged faster than normal people, and found articles online about the other girls dying from "old people diseases". She tried to get to the cure while developing arthritis.

I've been trying to remember this book series forever, so if anyone knows the title I'd be really grateful!

Answer 1

The Watchers series by Peter Lerangis

The books you mention are:

Lab 6:

Sam's parents are trying to extract his twin -- who's still inside Sam's body.

The Google book summary:

Something is wrong in Lab 6—what are Sam’s parents hiding?

Sam Hughes has always been too smart for his own good. It’s in his genes—both his parents are scientists who specialize in artificial intelligence—and sometimes it gets him into trouble. Sick of the bully who always steals his computer homework, Sam gives him a disk laced with a virus as a prank. To escape the bully’s wrath, Sam runs and hides in his parents’ lab. Inside, Sam hears a voice calling to him from behind a locked door labeled “Lab 6.” His parents are in there, and though he can hear them, he doesn’t understand what they’re talking about. Are his parents hiding a body in their lab? Something strange is going on, and Sam knows the answers lie somewhere in Lab 6.

I.D.

The watchers see things that others can't see. In this installment, a young girl discovers she is a clone...and has only days to live unless she finds the secrets of her creators.