After waking up and reading your post again I was reminded I should never try answering things when I'm extremely tired. Not only was I trying to answer a 5-year-old question but my eyes missed many words.
Sometimes the best way to discover something is to realize first what it's not. From your first two paragraphs alone it's easy to deduct that this was a book you read in the past but no longer have access to nor remember the name of. You do not remember the word or words the author used to describe these characters, and your use of characters is referring to a participant in the story. We can check off Star Trek's famous Android Data; Isaac Asimov's 'Positronic Robotic Humanoid' or 'Positronic Robot' in I, Robot; and since even in the third paragraph you never use the words organic or synthetic, because the easiest way to define an Android is a humanoid machine. They are machines that are made to resemble a human. So it's not the little boy or sex bots from AI, nor were they Roboti from R.U.R.;
Searching the depths of my mind and and sifting through any sci-fi knowledge it contains I'm left with three possible good options for the answer you seek. Because the definition of a cyborg is not to be humanoid, but that it's own limitations are enhanced by cybernetic organism or mechanical machinery, so it could have been some type of Artificial Cyborg.
To easily understand the definition of an Automaton just think of it as Automotion, or an automatic machine. An automaton is a machine or construct that operates under its own power. Automatons are famous in steampunk stories, where robotic machinery seem to come alive as it operates of its own free will.
But then we get to my last option witch I use as my educated answer due to your empathetic feeling of using the word machine to describe this character, witch makes me believe the author got you to react emotionally to a humanoid trait portrayed by the character; and golems, witch are constructs usually made of rock, clay, or metal, that have been magically imbued with artificial intelligence, usually with something like a gem that basically resembles its heart, or life force. To kill a golem you destroy that. And the one trait commonly used on golems is when it begins to seem more human when it starts showing an emotional sensitivity, compassion, or concern for one or more of the party it now follows, building a friendship and showing such a level of care and protection over them that they usually will sacrifice their own life to save them.
This question being so old and I can't find a user under the name Kplumber, probably means I'll never find out if I'm right or if maybe they were some type of artificial intelligent automatons, which if you think about it could also fit with what he described, I just like golems better, LOL.