2 slave devices to one system??
(3 TOTAL devices)
Yes, this is called a Piconet, which allows up to 7 active slave devices and 255 additional inactive (parked) slave devices.
More specifically, can I create my own remote which connects to my phone while its playing on its own or while its connected to speakers or something?
Are you asking if you can make one of your own design, or to buy one of the shelf? I think the answers are yes and no.
It sounds like this is what you're looking for, which should control the phone even when playing through bluetooth speakers.
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