so what? Cylons can have kids.
If anything, they're not Cylons because it's impossible for Tigh to be one, given that he was around way before the Cylons had the ability to make human-like copies. Which means that at least in Tigh's case a switheroo must have been pulled at some point...probably on New Caprica. But that would again be impossible, because if he's one of the Final Five even the Cylons wouldn't know about him, thus making it impossible for them to have actively made the switch.
But the Cylons could just have easily implanted them with...something, which is making them hear the music. My money is on Laura being a Cylon and some other explaination for the others.