an interesting idea, but I think by now that info would have leaked thru Lara. Earlier in the series, I'd have given it a better chance.
The WAG (an offhand idea, really; but we need
some reason that Raith Sr. had killed all his other sons, but Thomas lived to adulthood).
]Margaret could have hinted -- over the first few years of Thomas' life, where she was being Raith's "senior concubine" -- that she intended her son to
LIVE, and had laid some subtle and dangerous warding on Thomas. Raith figured (a) he had years to break down Margaret's resistance, before Thomas' first kill & the awakening of his Hunger; & (b) his own protections would likely suffice, anyhow.
Then Margaret went walkabout. That eliminated (a) ... and made Raith mad as hell: no woman should be ABLE to reject him! So he tracked her down and had her killed... and her death-curse got him despite his protections! Which, obviously, rendered (b) moot too.
And then Thomas showed absolutely zero inclination to "play politics." So Papa Raith played the long waiting game.
As for Lara -- Thomas ascribes her hands-off approach to him as being a limited bit of family loyalty... but what if she's worried about whatever protections Margaret left on Thomas?
Margaret LeFay escaped her father
at the peak of his powers, and then managed to land a curse on him that lasted for
decades. And Harry... well, Lara has seen Harry in action. He saw through her papa's charade, in just one night. He killed a bunch of baddies in the Deeps, including summoning lava
in Chicago. And then, when there was no way to survive, he saved them both. Lara was giving the sexuality her all... and Harry
used her for sex, instead of succumbing. He took the full force of a Whamp, and channeled it into his willpower in an entirely non-erotic fashion. At this point, Lara is likely
very cautious about the abilities of that family!
They have some anti-magic tech. Those arm wraps they used in the duels.
I think those arm-bands were a unique item, probably stolen, traded... even bought (from Svartalves?). They could even have been White Council work (I'm sure at least a few wizards have gotten Whamp-whammied over the years, and served the White Court in return for some o' that sweet, sweet luvvin' (or, as noted, straight-up theft)).
... put something similar looking inti his suits. When he is attacked they glow. They are not draining magic, he has them on battery power.
I don't have my copy of Blood Rites to hand (grrrr). I'd like to look at the descriptions of the protections on Lord Raith, vs the ones in the armbands. I don't remember them being similar (the glowy runes, etc).