What form does my friends stepson need to fill in to come to britain from jamaica?

My friend is married to a man from Jamaica. He is now a legal british citizen, they would like his 14 year old son to come over for a few weeks holiday in the summer, but cannot find out which visa form they need to fill in. I assumed it would be the family visitors form but she is not sure, when she was arranging for her husband to come over, the British and Jamaican embassies would not tell her, she had to go to a solicitor and pay thousands of pounds just for him to download a form off the internet, and obviously does not want to do this again, can anybody help?