The Three Are Living a Married Life is a Manga/Manhwa/Manhua in (English/Raw) language, Josei series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

On the night of her fourth wedding anniversary, moans were heard from her husband’s bedroom. “Tell me I’m better than her, come on.” It was the voice of her twin sister.