Im not an expert, but to put it truthfully, its gonna be pretty hard with those GCSEs. However, if you really want Oxford, you have a chance if your whole application is good, personal statement, admissions test, predicted grades etc. I'd say there is no harm in applying, you will gain from the experience whether you get in or not, but also don't be too fixated. You could have just as good a life if you don't go to Oxford for university.