Parents

This isn't strongly and clearly addressed in our tradition, and so there is a broad scope of interpretation.

From a jurisrpudential viewpoint, the main topic for obedience that is described is with respect to fulfilling the responsibility of the spousal bed, and anything else directly related to that.

Some people take a broader view.

Similarly, with respect to tafsir, some people take the word "obedient" (qanitat, 4:34) to mean a woman obeying her husband, others take it to mean a woman obeying God.

However it is worth considering that all of these elaborations on spousal obedience happened after the time of the Prophet and so there is some involvement of the author's cultural views. 

In my experience, in practice, marriages tend to fit into two models - a "master-slave" model (where one person commands and the other obeys) and a partnership model (where the two work together and discuss things mutually). I find in general people tend to re-enact the model they saw growing up and to some extent that which is culturally common around them. For instance, some cultures are quite patriarchal, and this is sometimes reflected. 

I have come to feel that this is one way where Islamic teachings are adaptable to a variety of ways of living and aren't wholly specific. However I am sure there are others who will give more specific views. 

In general, in Islam, one should avoid breaking ties with one's family unless there is a serious and overriding reason (such as fear for one's life). However, whether one wishes to maintain a close relationship or a more distant relationship is a personal choice.

I don't know the details of this situation. I would surmise that in most cases, if parents break ties with their children on account of their child's poor academic performance, it is due to (a) other issues, not just academics,  (b) an attempt to motivate the child to do better by "punishing" them, or (c) a projection of their own psychological issues onto the child. 

Anyway, all the child can do is try to be polite and respectful, try to avoid arguments, and keep the door open in case they wish to resume communication. 

If a young person is not doing well in academics, and has tried various ways to improve but has not succeeded, it is worth considering other options such as vocational school or going into business. Everyone has their own skills and talents. There are a lot of jobs that are not related to academics (such as being a chef or plumber) which pay well and are necessary jobs for society, even if the parents' dream is for their child to do something else.