Multi Store Setup single SKU

[malblack]

Hello,

I'm a bit stuck setting a multi-website / store configuration.

I have set 3 stores up on my localhost and can access their URL and it displays the correct store name, logo theme etc.

for easy product and stock management, the Default Catalog holds everything related to the categories, products with a single SKU per product
Default store will display ALL categories & Products we have.
Store 2 & 3 will only show the Categories & Product selected for that store.

When I add the items to the 2nd & 3rd store Magento is creating new SKU's and URL's for each category & product
Default store SKU: SGSABAG-BB
Default store URL as follows:
https://www.site-one.co.uk/category.html
https://www.site-one.co.uk/category/product.html

2nd store SKU: SGSABAG-BB-1-1
2nd store URL as follows:
https://www.site-two.co.uk/category-56.html
https://www.site-two.co.uk/category-56/product-231.html

3rd store SKU: SGSABAG-BB-2-1
3rd store URL as follows:
https://www.site-three.co.uk/category-86.html
https://www.site-three.co.uk/category-86/product-331.html

How do I get it so all 3 stores use the same SKU  SGSABAG-BB
and the following URLs:
https://www.site-one.co.uk/category.html
https://www.site-one.co.uk/category/product.html

https://www.site-two.co.uk/category.html
https://www.site-two.co.uk/category/product.html

https://www.site-three.co.uk/category.html
https://www.site-three.co.uk/category/product.html

Thanks in advanced