Will I be able to join the Zippi runs together to create a larger run?

We would not recommend this. You can find the Zippi Run extension packs here - https://www.omlet.co.uk/shop/rabbit_products/rabbit-runs-playpens-zippi-extensions/ 

Alternatively, if you are looking for a large enclosure for your pets you can find our Walk in Runs here - https://www.omlet.co.uk/omlet-rabbit-runs/