I'm sorry I wasn't clear enough, by "device" I meant the one connecting to the bluetooth speaker, and I wrote that before realizing you asked for help on the iPhone X forum, meaning your device was the iPhone X.
As I wrote before, to connect more than one bluetooth speaker to your phone you need speakers that support this, most probably through the app of the speakers (at least Bose and Ultimate Ears have apps that allow this with their speakers/headphones).
In my particular case, I use Ultimate Ears and their app, and I'm pretty happy with the results.