The baby might not need saving, remember a hunger dies if the Whamp falls in love and gains True Love Protection before first feeding. Technically this has happened here and the hunger and the baby shouldn’t have survived, the survival of the baby suggests something deeply strange is happening which might give Harry the info he needs to save Thomas hunger and not just Thomas. At the moment the hunger is too interlaced with Thomas, even if you could remove it Thomas would be wrong this is a lesson from Molly. The sword is a sword, not a scalpel, and it’s wielder hates operating on living people.
The baby is born in February/ March and to the whamps it is wrong to them , they call in Harry, and he perhaps call in Molly, and determine what is wrong, and it is that knowledge which will save Thomas. There may have been a medical reason why papa wraith killed his sons, a recessive tendency for his male offspring to become something else, not Whamp. The baby is what Thomas could become. He is around to be asked. He may know why Justine conceived in the first place, despite being under True Love with Thomas. Thomas consulted the family records, not his father who should know something.