Can employer see home network usage on personal device

I am just wondering whether it is possible for an employer to monitor usage on personal device on my home network in circumstances where a work device is also connected to the home network at the same time but not in use. I work from home occasionally and when I want to browse non work related things will use one of my own devices but often leave my work computer connected to my home network in this time.

How about in circumstances where personal phone which has had to install an app to secure it in order to access work emails on the phone is used as the modem, e.g. the personal computer and work computer are both hotspotting from the phone. The app does say they cannot see web history by installing it.