Not to be rude or anything, so I appologize if I come of so, but an 11 year old, or 8 year old, or most any child will not take care of a pet. Even when a younger child says I'll walk him every day and feed him and pet him... it invariably ends up the job of parents. (Not a parent, but personal observation).
Your father needs to step in and put his foot down. Anyone who is constantly loosing pets or having them get sick and not trying to take care of them, should not have pets.