You can replicate them to your existing Vnet but replicated VMs will have to be configured with new IP (Vnet) when you want to activate them.
Also, if you want to place replicated VMs in different Vnet, you need to configure VPN connectivity with new Vnet.
Please go through below link
https://docs.microsoft.com/en-us/azure/site-recovery/site-recovery-support-matrix-to-azure