Jayne,
Try this link:
www.angelman.org/ IT has several different categories from the home page, including one with info for families that is explained in pretty much plain English (rather than medical terms). Your grand-nephew should start to get services as soon as possible inlcuding special education, speech, and possible Occupational and Physical therapy. I am a speech therapist and have worked with kids who have Angleman's syndrome. The students I have worked with have not learned to talk, but they understand and some can use picture boards to communicate or learn sign language. Each child with Angelman's is different. He will learn to walk and the seizures may disappear as he gets older.
It is hard to explain Angleman's syndrome, it is not too common so you will probably get alot of practice at explaining it, the more you find out about it. The most important thing is that he is in a loving home with people who will do their most for him so he can become the best person he can. I can't stress enough that the sooner he starts receiving services, the better it will be for him.
Good Luck to you and your family.
Lisa