An Azure service that delivers high availability and network performance to applications.
Yes, you can create Private Vnet peering between all three Vnet, however it takes admin time. You did not talk about you production Environment. Are you planning to isolate that Vnet?
I do not know your complete use-case and technical requirements, however you should try App Service Plan (Standard Tier), using this you can created multiple slots for each environment, and you can swap deployment slots as you are making progress.