Spouse visa extension in UK (what documents needed )

[Vickzz]

Hi everyone,
My Mrs spouse visa is expiring in August so just want to know what documents are required for visa extension in UK. We also have one baby girl now who is British national so how much income we need to show ? Would it still be 18600£ or more as we have one baby girl now.
Would be grateful if someone can just guide me as it's been almost two and half years since she got her spouse visa and the process and documents required might have changed. Also what's the total fee plus nhs charge in total please.
Thanks in advance for any responses.