Dependant Visa - Help

Hi all,

First of all I am new to this site, but I read the forum previously and it was very useful.
My wife entered the UK (from Philippines) in September on a Fiance Visa, we have since married (December) applied for leave to remain and been granted the first extension. Unfortunately her son's Visa was declined, first as a dependant and the secondly as a visitor (for our wedding) - the reason given for refusal of her son, was lack of proof of sole responsibility. The Philippine agent we used did not advise us of the need to give evidence. Recently my wife's Ex-husband has given my wife a signed letter acknowledging she has sole responsibility for her son and his passport details as proof of ID
So I have a few questions, that I am hoping you will be able to help me with.
Question 1 - Which is the correct route - I assume it is a dependency Visa
Question 2 - How long does a dependency visa take to process
Question 3 - Apart from letter and passport from Ex, I am assuming that information provided would be same as previously submitted (although a solicitor did suggest that any photographic evidence of my wife and son together over the years will strengthen the case
Question 4 - What is the best method to employ - immigration agent or solicitor, any recommendations?

I appreciate any help and assistance you may offer as my wife is at her wits end and we do not want another refusal, thanks in advance - And can I say this site is quite amazing