The first book that I suggest to anyone dealing with alienation is Divorce Poison by Richard Warshak. This is a very thorough primer about what alienation is and is not, with lots of illustrative examples. Warshak writes with the authority of experience, and with compassion and understanding. He offers sensible and practical advice for dealing with a wide range of manifestations of parental alienation and PAS. I read and re-read it for myself, and have also found it useful to give to others (relatives, lawyers) who needed to hear about it from someone other than me.
It is available here: www.warshak.com/divorce-poison/index.html and should be in your local library. If it isn’t, recommend that your library purchase it.
It was first published in 2001 and there is a 2010 version with a new introduction and afterword.