The Buds cannot connect to multiple devices at the same time. It is easy to switch between Samsung devices (I have not tried this myself). Otherwise, you always have to disconnect and reconnect to the new device (I did this once and found it too complicated).
See also:
https://www.samsung.com/de...
You can't, but if you've already connected them to the device, you can just select them in the Bluetooth settings and they connect within a few seconds.