Interesting! I'm not a twin, and have never had twins among my good friends, so this is guesswork:
* Give them totally different names
Yes, if possible; not so different that it's obvious what you're doing.
* Give them different names but with a similar / opposite meaning.
Like
Dawn and
Eve?
Blossom and
Fleur?
Deborah and
Melissa?
Beatrice and
Dolores? I like some of those names better than others, but I really don't like the idea.
* Give them names that start with the same letter.
Only if you'd have chosen those names for non-twin siblings. And only if they have different initials for their middle name/names.
Laura and
Lucy, yes.
Laura Gillian and
Lucy Angela, maybe.
Laura Margaret and
Lucy Maria, no.
*Give them names that end with the same sound/letter
Interesting.
Helen and
Susan, no;
Helen and
Suzanne, for some reason, yes. Perhaps it's just less obvious when a different syllable is stressed. And, I once knew an
Ian with a brother who was
John - could never make sense of it.
*Give them names with etymologies from the same language.
Anne and
Ruth! Or
Mary and
Rachel, though I don't like them as much. I don't really mind where the names I like originate, though I do tend to prefer classic English, well-established ones.
Gerlinde and Irmela? Too non-English, though I like them both.
*Give them names of famous sibset, couple (real or fictional).
Oh dear, here come
Elizabeth and Fitzwilliam!
Romeo and
Juliet!
Brad and
Janet!
Frank and
Rocky!
I suspect that naming twins is much like naming singletons - at first, it doesn't occur to the child to like or dislike its name. Then the name is disliked and the parents get the blame. Then the name is liked or at least accepted, often being used in a nn form: no longer
Antoinette but
Toni.