thanks to both for your answers.
My stepson has even got my name as we changed it by UK deed poll, so his passport is in my name. The problem seems to be with the birth certificate which obviously states his previous surname and his biological father. According to the HR guys the law must have changed in qatar lately and the same name in passport is now not enough to guarantee the family visa. We have spent all day ringing solicitors trying to get something sorted but I don't know if we will be successful. If they had only told us before! we are due to fly in 5 weeks and don't know whether this will get sorted....