WooCommerce, Multi Shipping fees but not to be optional

Hello. I have set up multiple shipping options as follows:
– Weight based shipping – Which works corrects
– Flat rate of £1.60 when purchasing biltong knives – which works correctly
– Free shipping – with valid coupon code.

I’m having a couple of issues. Firstly I need the coupon free shipping to work only for weight based shipping.

Secondly, in the basket the shipping is coming up as radio buttons so the shopper can select their shipping. I would like this to automatically work out and not allow them to select which shipping.

website is sussex-biltong.com. The knives have been loaded but you cannot access them from the front end yet. Here is a link to one of them for testing – https://www.sussex-biltong.com/product/opinel-no-8-classic-originals-carbon-steel-knife-with-sheath-gift-set/

Please can someone assist me with this issue or point me in the right direction.
Many thanks, Lisa

The page I need help with: [log in to see the link]