Products page help

Hi, Im trying to recreate the following page in WordPress (https://www.medsport.co.za/prod_ssb_arms.html)

Currently stuck on the following code:

[Code moderated as per the Forum Rules. Please use the pastebin or post small snippets between backticks.]

What i need wordpress to do:
For the Next a Previous links to only cycle in the specific category e.g (Category: – Knee, once the number of posts exceeds 12 the next and previous links should only cycle through that specific category )

My categories are currently setup as follows:
Products (Parent Category)
SPORTS & SURGICAL BRACING (Sub Category of Products)
Arms (Child category of Products)
Back (Child category of Products)
Knee (Child category of Products)
Lower Leg (Child category of Products)
Shoulder (Child category of Products)
Upper Leg (Child category of Products)
Neck (Child category of Products)

Not sure if this can be achieved with one custom products.php and a single_products.php page.

Any help or source will be much appreciated..

Thanks a mill