There's something about Justine (PT and BG spoilers +WAG)

[Mira]

   If it is accurate, she could be off one way or another as far as to how far along she is.

[Helga Ozark]

I don't think that there's anything special about incubus wamps that Papa Raith hates other than competition. In BR (I think), Thomas says that his father controls his daughters by feeding on them (which is icky) but he killed or arranged the deaths of his male offspring because "his tastes don't run that way". He doesn't control his sons by feeding on them so they are a potential threat to his power and can overthrow him.
I like the cupid angle. Maybe Maggie senior arranged something with Thomas the same way she arranged for Harry to be starborn.

Anyway..I definitely think we are being misdirected in some way. There are constant references to Harry's father, a stage magician and they are all about misdirection so there is something that's hidden in plain sight for us....whether that's Justine, her baby or something else.

[Bad Alias]

Nemesis allow one to act without the normal restriction. Cat Sith wants to kill Harry from meeting him, he literally can’t because of his oath to Mab. Mortals operate under free will, it is pointless nemfecting them.

The normal restrictions on mortals is different than for fairies. If we take your first sentence as correct, then the assumption isn't that there's no point to infecting mortals; it's that infecting mortals will allow them to act without the normal restriction. The question then becomes what is the normal restriction for mortals.

[Conspiracy Theorist]

There isn’t one, it’s free will, though I suppose mortals could be used as disease vectors to get to a more powerful entity. A Nemfected Whampire, the closest monster to a human, would probably lose the True Love Protection restriction. Lara therefore isn’t Nemfected. With Wizards its probably losing the power lost on swearing on their power and breaking it, or being able to cross a threshold without losing their power Eb asks to enter Harry’s temporary apartment. It strikes me that the domestic bliss of Thomas Apartment, with Justine and a baby on the way mean’t that his apartment had a threshold, and a normal wizard couldn’t enter or push through a spell into the apartment without drastic power loss.

Suppose Thomas Apartment was being survielled by a wizard because it originally didn’t have a threshold, but one started forming when the baby was conceived? and a family came into being. That would reduce the surveillance a wizard could do and they would have to resort to more mundane methods. That may explain the lack of magical residue, and the need to attack the main Raith residence (no threshold) instead for information despite the heightened risk of being found out.

[Mira]

Suppose Thomas Apartment was being survielled by a wizard because it originally didn’t have a threshold, but one started forming when the baby was conceived? and a family came into being. That would reduce the surveillance a wizard could do and they would have to resort to more mundane methods. That may explain the lack of magical residue, and the need to attack the main Raith residence (no threshold) instead for information despite the heightened risk of being found out.

  Thomas' apartment is his and Justine's home, ergo it has a threshold.  That is some protection, against some invasions but not all, for that one needs wards.  Thomas doesn't have that kind of skill and apparently he never asked Harry to put them on.  However a threshold means nothing if whoever or whatever was invited in, that wouldn't leave any magical residue either.

[Conspiracy Theorist]

Wards are for when you really don’t have a threshold, a bachelor living alone in a rented temporary apartment generates a de minimus threshold. The BFS and Edinburgh headquarters need wards because they are nobody’s home. Karrin’s home has a threshold but requires additional protection. The Carpenters have an enormous threshold, but that is weakening as the children grow up and leave home, hence the Angels Thomas living on his own none (monster) Justine moving in de minimis, her establishing it as a home, slightly more. Making a home for a baby kerching meaningful threshold.

[The_Sibelis]

🤔 wards are for everyone. most wards are specifically set upon thresholds to draw power from them, this is how Dresden's operate. How the BFS sets wards on everyone's house.. Edinburgh only has wards because they have those stone things that can power them independently.
Wards without thresholds are generally one time use.

[Bad Alias]

Wards are for when you really don’t have a threshold, a bachelor living alone in a rented temporary apartment generates a de minimus threshold. The BFS and Edinburgh headquarters need wards because they are nobody’s home. Karrin’s home has a threshold but requires additional protection. The Carpenters have an enormous threshold, but that is weakening as the children grow up and leave home, hence the Angels Thomas living on his own none (monster) Justine moving in de minimis, her establishing it as a home, slightly more. Making a home for a baby kerching meaningful threshold.

It's implied Thomas has a threshold in Cold Days because he wonders how Cat Sith was able to enter uninvited. Harry normally anchors wards onto thresholds. See Harry's discussion of his wards on the storage container in Turn Coat. Marcone's castle has a threshold. Harry said so in Ghost Story. Edinburgh has people living there. I don't know if it's enough to form a threshold of any magnitude.

Wards are for everyone who can get them.

[Mira]

Wards are for when you really don’t have a threshold, a bachelor living alone in a rented temporary apartment generates a de minimus threshold. The BFS and Edinburgh headquarters need wards because they are nobody’s home. Karrin’s home has a threshold but requires additional protection. The Carpenters have an enormous threshold, but that is weakening as the children grow up and leave home, hence the Angels Thomas living on his own none (monster) Justine moving in de minimis, her establishing it as a home, slightly more. Making a home for a baby kerching meaningful threshold.

That isn't true, if I remember correctly Harry says, including his place, that while bachelor homes are less strong, there is still one.  I also remember that Elaine reinforced the the threshold for the paranet.

[Conspiracy Theorist]

Thomas’s threshold would be piddly like Harry’s was, as a bachelor it certainly didn’t stop the Toad Demon etc. Harry ended up getting a steel door, and warded up the Wazoo (a technical wizarding term). It’s a big difference losing 5% of your power as opposed to 95%. It is interesting though that Whamps can threshold.

The issue is when a threshold is strong enough to force a Wizard to leave most of their power at the door, or significantly depower a spell sent through it, and thresholds are variable changing over time and circumstance. Mort split his house into home and business to maintain his threshold for example.

[The_Sibelis]

Harry had to leave his power at the door to even go into an apartment in WN, which is a piddly threshold indeed... And Morts whole threshold was damaged by linking business with home too....

[Mira]

Thomas’s threshold would be piddly like Harry’s was, as a bachelor it certainly didn’t stop the Toad Demon etc. Harry ended up getting a steel door, and warded up the Wazoo (a technical wizarding term). It’s a big difference losing 5% of your power as opposed to 95%. It is interesting though that Whamps can threshold.

If I remember correctly the Toad Demon gained access to Harry's place because Susan innocently opened the door for it, which was the same as inviting it in.  An invitation cancels threshold and ward protections.

[Conspiracy Theorist]

Opening a door is not enough, there has to be an express invitation, see the occasions where Harry has asked to be invited.

[Mira]

Opening a door is not enough, there has to be an express invitation, see the occasions where Harry has asked to be invited.

Just went back and checked, the threshold did stop it for a while, it had to gather strength to break through it.  Then Harry's circle down in the lab stopped it cold, except Bob accidentally on purpose
sort of directed Susan to drink the love potion instead of the escape potion.  As Harry said a three foot circle isn't enough room for things like that.. Bob did get the escape potion to them only after he got a 24 hour freedom pass.

[Conspiracy Theorist]

Yeah because Harry had a piddly threshold, had that been the Carpenters, the biggest threat of Toad crossing the threshold would have been slipping on the the ectoplasm before it sublimated. Not all thresholds are equal and Jim has been deliberately vague on the point in book to give himself wiggle room.