Dhampirs exist only in 2 Books n
There're only 2 books that have Kindred Dhampirs in them: Time of Thin Blood, which is the actual main source, and Becket's Jyhad Diary, where there is one mention of them. The other Dhampir book is not about Vampires, so can be ignored.
So, let me grab my ToTB to look up what that tells us.
First of all, Vampires aren't suited to have kids in the first place, and the rate of mortality due to the parents (and their surroundings) will mean that almost none will ever get out of childhood:
With so many perils, it’s all too easy for a dhampir to end
up abandoned or orphaned at an early age. Dad runs off and
Mom dies at the hands of the scourge. Or Mom succumbs
to drug addiction and Dad decides his child will be happier
“among normal people.” That is, assuming Dad was ever
told about the baby in the fi rst place. Even if the family is
intact (for now), their prospects for domestic bliss are slim
in the World of Darkness. 1
Now, how does the Vampire society react in general? Well, a Part of the Camarilla doesn't believe they exist, But those that are in the know have to consider them as what they are: either they are an uncontrolled ghoul, or a breach of masquerade. In both cases, the prospects are not rosy and a cull order might be dished out very quickly.
Dhampirs are a new phenomenon in the World of Darkness. [...]
The existence of the dhampir is
still contested by cynics, who suspect some kind of millennial
hoax, but to those who have an inkling of thin-blooded
oddities, the idea is all too plausible.
At present, a dhampir who falls into the clutches of a full
vampire will most likely be mistaken for a revenant or a masterless
ghoul — hardly cause for joy, perhaps, but good fortune indeed
compared to the lot of the dhampir who is recognized for what she
truly is. To Camarilla vampires, she is the ultimate Masquerade
breach: an elemental and irrevocable mingling of Kindred and
kine. [...] To Sabbat and other
die-hard Noddists, she is an ominous portent of doom [...]2
That's the quite general broad strokes, from which the very same book carves a few exceptions just in the next paragraph - though even those are not too rosy prospects as being deemed a prophet of Gehenna is not good for long term survival.
Now, pages 81 and following have the rules for Dhampirs: you build a Revenant, but instead of a Ghoul you got a 15th generation vampire parent. In the pre-V5 plot, this would make the character at oldest 20, when the first 15th gen vampires appeared. This might need to be adjusted for the V5 timeline.
So far, V5 has no dhampirs
None of the V5 books published until February 2024 has shown or discussed dhampirs.
- Time of Thin Blood (1999), p.48
- Time of Thin Blood (1999), p.49
Note: While Half-Damned Dhampir (2000) exists it handles Kuei-Jin offspring in a Kuei-jin environment, not Kindred offspring. They don't generally exist in areas where the Camarilla has any power: wherever Kuei-jin Dhampirs exist, the power of the night is generally in the hands of the Kuei-jin, and Kindred are killed on sight. Atop that, Kindred wouldn't have a chance to spot those as anything different from Kuei-jin.
Best Answer
From what I have read. (most of if not all my information is 5e) When thinbloods diablarises a full kindred. They become a full kindred of one lower generation and the victim's clan. (this depends on if they are successful or not. Like all diablerie.) They lose their thinblood merits. (Day drinker, thinblood alchemy and all that.) They also lose their thinblood flaws. (vite dependency, dead flesh and all that.)
Discipline affinity. Depending on your storyteller you should be able to keep it. You will likely have spent EXP on it. You might even be able to spend EXP from the diablerie on it if the diablarised Kindred is proficient in it.
Now for a thinblood diabolizing another thinblood. Mechanically thinblood have zero in blood potency. So it becomes a humanity V resolve roll. (the one committing diablerie rolls humanity the victim rolls to resolve.) for every success. you get five EXP to spend immediately on Blood potency (up to the victim's blood potency. So zero.) or a discipline they are proficient with. As thin blood alchemy is treated as a discipline I would argue you could spend those point on it. Same with your discipline from discipline affinity. (it may be up to the Storyteller whether the Thinblood alchemy's distillation method effects this.)
The rules are written in a way that allows room for interpretation. I hope you have fun and that this helps.