Hi folk,
I have started moving my old wifi switches to zigbee, I have a Sonoff zigbee usb dongle connected to HA and integrated my first 4 switches fine but I can’t seem to get them to be exposed to google home, which is a big issue 
(wife has a nest hub she controls lights etc. and if it doesn’t get the approval it goes…)
Can I have zigbee devices on HA and expose them to google home (the wifi devices are connected to HA through tuya local and the tuya app is exposed to google home)
Yes, if you have Home Assistant linked directly to Google Home. But reading your question again, through local Tuya, I think no. See my edit at the bottom.
When you go to Settings, Voice assistants you may have set the option to automatically add new devices off, or turned automatic synchronisation off. Here you can see and control which devices are exposed:
Regardless of the automatic addition setting, the entities themselves have a setting too, so that can be an easier way if you are looking for a specific one:
If Home Assistant does not sync the devices immediately to HA, you may need to ask google home to sync your devices.
EDIT: Reading your questions again: you link devices with local Tuya and hope to have Tuya sync those to Google Home. In that case Tuya is responsible for exposing them to Google Home. I doubt that will work if local Tuya is what you use, because I would not expect Tuya to expose local tuya devices to cloud. As far as I know local Tuya is built to expose Tuya devices to HA and not the other way around. I doubt you’ll see HA zigbee devices in the Tuya app, let alone have Tuya sync them to Google via cloud.
If that is what you meant, I would advise to link Home Assistant directly using Nabu Casa or one of the many other guides. That way you are not depending on Tuya.
I think the devices are both in the Tuya cloud (for Google Home) and local Tuya (for HA)
For Zigbee, you would need to use the Google assistant integration