My mum has said that my step dad dose not have prenatal rights over his daughter because he left for 6years and my mum was in hospital and my sister and brother went to live with my nan he did not sign anything to give up the rights so dose he still have them

Only the courts can take away rights, and he does not love them merely for not visiting or being around.
The mother could have course file to take some away ( depends on the state, in GA for example merely not paying support or not visit is not enough to take rights away)

And of course mom does not like dad, so she will say what she want you to hear.

If the dad wants custody, he will have to file a motion in court asking for it.