Hi, I’m not from Australia, but I have a few suggestions.
WiFi light switches and bulbs are, to be blunt, a pain in the ass compared to z-wave and zigbee when it comes to working with a hub like hubitat.
I’m sure there are some users in Australia that can help confirm whether the brand you’re referring to can be integrated with hubitat, but most likely some type of firmware flash to the bulbs in question would be required, if they can be made compatible at all.
The hue devices can continue to work with hubitat just like they do with the echo plus hub. And yes, hubitat can control hue devices without an active internet connection as long as the local LAN is functioning.
Devices paired to hubitat can be controlled directly by asking Alexa without having to use an incantation like “tell hubitat.” However, Alexa doesn’t work without an internet connection, even though hubitat can maintain control of your devices when the internet is down.
Edit: actually just to clarify, your sister has a hue bridge and bulbs along with her echo plus hub? Or just hue bulbs paired directly to the echo plus?
