HMRC document to prove £18600 - Self employment

I am applying Set (LR) in August this year and FLR (M) for my wife and for this we have to meet up the financial requirement of £18600. Currently I am on PSW visa and she is my dependent, however she came originally in August 2011 as Tier 4 dependent.

My wife is teaching students abroad via online and has recently declare / register this to HMRC as a self employed tutor / tuition provider for 2014 / 15 tax year.

My questions are:

• Can I add-up her income with mine to meet up this income threshold of £18600?
• Secondly what document does she need to provide as self employed in support to meet up this income threshold?
• Or what documents should we demand from HMRC which evidently fulfil the requirement of self employment and financial threshold of £18600?
• Do we need to get professional accountant for this?

Yes you may combine earnings.

See Annex FM 1.7 (click) for your remaining questions.