You can't train a grey to like or dislike someone. It is the particular grey's choice. Some greys only like one person, some like more than one, some will only tolerate other people. It depends on the grey. It is not always the person who cares (feeds/cleans the cage, etc.) for the grey. I live alone and my grey loves me and is leery of others. When my family are over, she accepts them but will only fly to my nine-year old grandson and land on his shoulder (which I immediately remove her from). She for some reasons likes him. I remove her from his shoulder as I do not want her to bite him.