How Can ADHD Be Treated?

My daughrtbin law diagnosis my 4 year old grandson with ADHD and I ve been around him sinnce he was little . She s taking him for testing which she also did at 3 . He can sit and play for hours . He told me he has a mom but she doesn t do anything with him . They moved and had another child and all he hears is I have to do for him who is now one . He has to share all his toys and his brother destroys it and he gett and and does get mad and shoves him hard , I noticed it more when they had him on melatonin , he was agessive , mean and had horrible night terrors , I know she has given it to him since he was 3 months without telling her doctor . He s good kid and he doesn t need medicine, I watched him in preschool and he behaves, sits and does his work . His parents are either on phone or computer from time they get up till bed time . I m worrried about him and don t know what to do as they will not tell the doctor I have had him and his brother , he s not mean to him when he s with me