I can field a couple of your questions in here, though its still valid that the game doesn't explain them.
Cambions are direct half-devil offspring; very powerful individuals, but not full fiends. I believe a Cambion doesn't quite benefits from fiends' functional immortality, but they don't really age like mortals either.
Tieflings are mortals with fiendish blood in their heritage, but not nearby. I think the *maximum* amount of fiendish lineage a tiefling can really have is 1/8: that is, three generations down from first contact. They are just normal everyday people, who express fiendish visual traits, and sometimes manifest a few minor powers, but no more 'potent' than any other mortal race.
As for the drow mess... I made a thread about that myself. Drow are a subrace of elves, full stop. Anything beyond that is social/personal/spiritual and is not apart of their race.
My halfling has "Lightfoot Halfling", "Halfling", "Female", "Custom Character", "Halfling", "Lightfoot Halfling", "Baldurian"..... Sooo... They really do need to fix up their tag system.
For the rest, all valid issues and concerns, well raised. My support.
If a cambion is a half fiend and a tiefling is at least 3 generations away from their fiend parent,
then what are the children and grand children of cambions?
- I could ask the same question about half elfs:
It is clear when one parent is human and the other parent is elf but
Does half elf imply what the other half is? Same for half orcs and other half races.
I have 3 questions that are not 100% serious
Question 1: If your mother is an elf and your father is an orc you are both a half elf and a half orc, which stats and bonusses do you get?
Question 2: So if your mother is an elf and your father is a fiend you are both half elf and cambion?
Question 3: I see many halflings, what is a ling? Whatever it is, it must be rather small.
Fun fact: Species is defined as a group of individuals who can have fertile children together.
So with a few exceptions, almost every sentient creature in the DnD universe belongs to the same species.
Just look at the sorcerer bloodlines, your ancesters could be anything, demons, angels, dragons, fey, snakes, undead and totally alien stuff.
Maybe the term "race" is correct.
Like there are many dog races that differ a lot in look and size, but all of them are dogs.
So I want to play this char:
I am a half elf and a half orc because my my mother was an elf and my father was an orc. I am very beautiful because the granmother of my mother was a nymph (my mother looks like an elf and the rest of her family are elfs, at least as far as I know). One of my grand-gradfathers was the result of devil + dragon who had a child with an orc while one of my grandmothers was an ogre. This means I am also a tiefling. So I am not only beautiful but also very strong and tall. I chose to become a bard.
Does anybody seek an actor who is 3 meters tall, has the face of an angel and wings like a dragon? Do not mind that my skin is a mix of green and red, some make up can fix that.
Prof. Dr. Dr. Mad S. Tist 
