The tethering itself is still WiFi. BT is only used for the handshake.
No shared text messaging at all.
SMS is backed up to OneDrive, that's pretty much it. Its even invisible in OneDrive directory on Onedrive.com or your SP3, so you can't manage anywhere but on your Windows Phone.
There might be an app that enables such feature like the Android app you mentioned, but I dont use SMS much, so I dont know.
No shared text messaging at all.
SMS is backed up to OneDrive, that's pretty much it. Its even invisible in OneDrive directory on Onedrive.com or your SP3, so you can't manage anywhere but on your Windows Phone.
There might be an app that enables such feature like the Android app you mentioned, but I dont use SMS much, so I dont know.