How many dependants does she have? - Do you and your wife planning to bring them all in the UK?
You both have to provide lots of evidences and she'll have to prove to the embassy that her 15 yr old brother has no other family than her, I mean we are talking about her 'brother' in this case and not her child. Your wife must show evidences that she is sending money to his brother in the Phils.
I think you both should see a professional adviser.
