There is actually someone that posted all about their Breath of the Wild cosplay here
, if you want to see it!
They seem to go through and talk about every bit of their costume so maybe it will help you get started.
This tutorial may also help you?
A good way to think of Link and his tunics is just big t-shirts with annoying collar shapes!
Simplicity has some very good patterns which may also be a good place to start with this.
They are Simplicity 5069, Simplicity 1461 and Simplicity 5197.
Of course you would have to alter the pattern's sleeves, length, and other various parts of them according to your husband's measurements but I hope that the links I have given you at least help you get started!