I have just purchased the Eufycam e two cam system and I would like to add a video doorbell, my question is can I add the add on battery video doorbell to the homebase that comes with the cam kit I have purchased or do I Need a separate homebase, just a bit confused 
Your Cam 2s came with Homebase 2, so you can add a Video doorbell to that. I have Cam 2C’s, Homebase2, and a Wireless T8210 doorbell and it all works fine. There may also be a Wired doorbell that works with the the homebase 2, but not sure about that.
Be careful that you don’t get one of the doorbells with internal storage because they won’t work with the homebase.