My 4 year old son and 2 year old daughter play with my 3 year old niece quite often. My niece happens to be very bossy, always shouting commands and "making" my daughter do what she wants by picking her up, and so on. My son has reached his limit with her and won't share toys, won't include her in play and has become very protective of his baby sister. My sister-in-law has taken this personally and sees my son as the rude child. I encourage my son and daughter to use manners and include their cousin, but I also cannot force them to want to play with her. Any suggestions as to how we can make this a more harmonious relationship???? Thanks!!!!