Jaquta gave you the right advice...
You have already received the best advice...you might ask your doctor to help mitigate the symptoms by prescribing some short term use of klonopin.
Your doctor is right...if you don't have a middle ear problem, the airplane ride will have no effect on your ears....but you need to be in therapy to get your life going on a better track in order to face your anxieties, rather than be defeated by them.
The best thing you do for yourself is to do battle with your phobias and begin to find a life of independence. You must get help to challenge these fears and find a way to leave the house and find work...independence is precious, and give you new options...get the help you need and keep your focus there instead of on your grandmother.
You should see a psychiatrist to find the origin of your anxiety...depersonalization is a symptom of anxiety, and there is a source, and you will be better off knowing that source than trying to just damp it down with medications alone.