If the product of a union between two elven sub races( sun elf/ moon elf for example ) is either one or the other and not a combination of the two heritages, would the offspring take the surname of the parent whose sub race they are?
That would be one option. It depends on a lot of factors.
* Did one elf marry into the other elf's family or clan? * Does one elf have a famous/important lineage and the other doesn't? * Is one elf significantly higher status than the other? (i.e. a temple matriarch marrying a vagabond) * Which elf is actually raising the child? (i.e. single parents would probably give their own surname) * What does the child want to do, once they get old enough to make an informed choice?
There are a lot of reasons an elf would have one surname or another.
Doggedly converting 3e back to what D&D should be... Sigh... And now 4e as well.