Blues:

There are a number of requirements for two voices to "blend" and by that we mean the ability to sing close harmony like the Louvin Brothers or the Everly Brothers.

One is that both voices must have the same accent or speech pattern. Imagine a singer from Brooklyn, NY trying to "blend" with a singer from, say, Mississippi with a southern drawl.

Another is that you have to practice a lot (and we mean a lot) to get your phrasing precisely the same. This, of course, comes easier to siblings who have sung together all of their lives.

Another is that you have to sing in approximately the same range because close harmony means that the harmony notes are very close to the melody notes. Last night while we were reading this thread we were listening to the closing act of La Boheme where there is a duet between Rudolfo and what's her name. The sound was beautiful beyond belief but no one would say that their voices "blended".

In your opening post you said that your sister's voice was that of a well trained, schooled soprano. Her voice training probably makes it impossible for your voice to blend with hers because she no doubt uses a lot of vibrato and pear-shaped tones with an emphasis on vowel sounds and practically no consonant sounds. You, on the other hand, probably don't do these things especially if you have a "good blues voice". Also, your range is undoubtedly much lower than hers and octave differences can sound nice but they don't blend.

Although we did not sing when we got married, we were brougt up in the same place and have the same accent. Also our voices have nearly the same range. Couple that with 43 years of singing together and, voile, a blend.

It sounds like you need a different singing partner!

Bev and Jerry