How do I make a custom brush from a beard?

[chrissydetroit]

In the first photo I used a beard brush that a Youtuber had for download but I want to create my own beard brush (hair strands) because as you can see in the pic, the brush isn't thick enough for me to make his beard look more full. The second pic is the reference photo that I want to use for a beard brush. The last pic where the arrow is pointing is what the brush looks like when I use it. The brush doesn't look like actual hair strands. It looks like a regular hard brush. Can someone help with this? Thanks in advance.