SPOILERS FOR THE HARRY POTTER BOOKS, I SUPPOSE
Now I don't know if you will ever read this, and you might have found out about it already, but in the "canon" Harry Potter books, Squibs and Muggles are different, in the sense that Squibs are Wizards that cannot cast spells but can still kind of interact with magic. For example, in the fifth book when Harry and Dudley are attacked by Dementors, Dudley is unable to see them, and thinks that him feeling cold and dread is something done by Harry, to the point that Dudley punches Harry telling him to stop, while later on, during the trial to choose if they should expel Harry from Hogwarts or not, Mrs. Figg, a known Squib, is able to describe the appearance of Dementors, showing us that while Squibs cannot cast spells, they are still "magical" in some way, able to interact with the magical world. (Now, to be fair, someone, like Dumbledore, could have simply described to Mrs. Figg what Dementors look like, but this is never called into question and seems to be accepted as evidence during the trial, so it stands to reason that Squibs can see them).
SPOILERS FOR THE FINAL CHAPTERS OF THIS FAN-FICTION, I GUESS
First of all, glad to know I'm not the only ones that feels compelled to read this masterpiece more than once. Second, no, you can't lie in Parseltongue, if you read the last chapters Tom, since calling him Voldemort or Quirrell feels weird, says that his original plan was to make Harry/Other Tom the ruler of magical Britain, and fight each other like two retired old friends would play chess, but unfortunately, or fortunately, he heard the prophecy that said Harry would tear apart the very stars in space, got scared, and changed his plans to kill Harry to prevent this future from happening, not that it worked.