For wired headphones there are headphone splitters but for bluetooth I think you need a Bluetooth adapter.
There are some in form of PCIE cards, which provide WiFi and/or Bluetooth, however, you want to use them on a laptop so they're not compatible with your use case.
Some are small USB dongles and depending on model allow more than one device to be paired/connected. The USB dongle ones are usually around $15-20. Like this one
here.
Some are bigger than dongles and are like USB flash drives, some have external antennas too. Some of these just have a broadcast mode and just allow audio transmission to headphones or headsets which is basically what you want I guess. Like this one
here.
Apparently some of there are only...