The word "coetaneousnesses" may seem daunting, but its spelling can be broken down using IPA phonetic transcription. The first syllable, "co," is pronounced /koʊ/ like "koh," the second syllable, "e," is pronounced /i/ like "ee," followed by "ta," pronounced /teɪ/ like "tay," and "ne," pronounced /ni/ like "nee." The suffix "-ousness" is pronounced /əs.nəs/ like "uh s-nuhs." Therefore, the correct spelling of "coetaneousnesses" includes all of these sounds and syllables, making it a complex but valid word in the English language.
There doesn't seem to be an etymology for the word "coetaneousnesses" because it is not a commonly used or recognized word in English. It appears to be a highly specialized or perhaps even a nonce word, which means it is created for a specific purpose or context and may not have a widely established etymology.