I did a trial run for the eclipse yesterday on my backyard. Both my Android phone and an Android tablet were connected via Seestar app simultaneously, and there was no problem at all. I disconnected them and reconnected to Seestar's wifi several times, all while taking a timelapse of the sun, and each time it took a few seconds to automatically get into the Solar mode and show the same picture. Note that it will be controlled from both devices simultaneously, so if you give a tablet to kids, they can command the Seestar to turn away from the sun, or stop the timelapse etc.
I also connected my Windows laptop via RTSP stream. VLC player supports RTSP. As long as it's connected to the Seestar's wifi it streamed just fine. The only downside is that the video is vertical, and there is no zoom in any of the RTSP-supporting players. So sun appeared smaller than on a tablet. But you can stream to any number of devices... So if you can find a player that supports RTSP on any tablet, you can use that without the app.