[Elladan and Elrohir]

As for the original question of this thread: How pointy were Elrond's ears?

Hard to believe no one has mentioned GENETICS to this point, but the answer is to be found therein. The offspring of an Elf and a Man will NOT have "half-pointy" ears; he will either have ears that are fully pointed, or regular Man-shaped ears. There is no way to tell with Elrond since his genetic pool is about evenly divided as far as Elf and Man ancestors go. We can assume that his ears were fully pointed since he was grouped with Elven-kind, and yet he only made that choice after the end of the First Age.

Hmm...to be facetious, I think I've just found the reason Elrond chose to be of Elf-kind and Elros chose to be of Man-kind: because their ears perfectly suited them for it! Elrond's were pointed, and Elros' weren't! THEY'RE NOT IDENTICAL TWINS!!! AAAHH!!!

Seriously, there's no way to tell for sure, as far as I can see. Which isn't very far.