A good tip for learners of English is "if you can't see it, you can't i-n-g it!". This means that any verb which you cannot see someone doing cannot be used in a continuous tense. For example, you cannot say "he is having two brothers" because you cannot see this just by looking at this guy. Also, you cannot say "I am wanting something" because I cannot see you want it. It is the same for every continuous tense.