Wife visa as dpendent

Hi, my friend got ILR recently, now he wants to bring his wife and daugther(2years old) in uk
He is a taxi driver and self employed.He earning was £35000 last year and he paid all tax in this earning,also have SA302 form from HMRC as proof.I am aware he needs to show about £22000 for his wife and daughter, He is planning to apply after 3 months from pakistan ..my question is

what documents he need to show for his wife and daughetr in term of earning?
as he has no salary slips,so how can he satisfy CW about his earning?

i know about english lanuage requirement for his wife, quick response is much appreciated.