I will be going to Bangkok next week to apply for a holiday visa for my wife and her daughter, our daughter has dual nationality so she is ok.

We will be going to the UK to visit my mother and the rest of my family for 2 weeks.

Do i need a letter from my mother as we will be staying with her for the 2 weeks.

On the application form it ask's about employment details, well my wife does not work as i support my family, i will be funding the whole trip. Do i need to show my bank details and work payslip's as supporting documents for the application.

Thanks in advance

Basically, yes to everything.

Your wife will have to demonstrate that she has enough money for the trip and sufficient accommdation. The money does not necessarily have to be from her own funds, but the person providing the wherewithal has to show that they can afford it. A letter from your mother offering a place to stay would top things off nicely. Also included evidence of your status in Thailand.

Scouse.

See also the supporting documents sections in the Sponsors and Vistors guidance from the Application forms and guidance page.