OotP: Family Trees, house elves

[innovan]

No: HPFGUIDX 63045

OotP Spoilers
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Confusing things:

Bellatrix Lestrange calls Harry a half-blood. Is she stupid? Malfoy 
has all family trees memorized, you think the rest of the D.E. would 
as well.

The Weasleys are not on Sirius Black's family tree because they are 
"blood traitors". Does this mean they were disowned by their families? 

House Elves are sworn to serve a family line. Are the Weasleys denied 
house elves as part of being disowned by their families?

"Innovan"