This is really a group of questions that cannot be dealt with in a Forum such as this - the topics are simply too great to address. Suffice it to say that all three of the topics are types of major transitions within a family. Changes in a child's environment, such as would occur in all these instances, can (but do not necessarily) result in unstable behavior, regression, disorganized behavior. Children do best when their environments are stable and consistent. When change occurs, stability and consistency are threatened.
Thank you so much, you have really helped me :)