It sort of depends on what you really want/need, your programming skills, etc. Note, while I know these products exist, I might not have actually used them.
If you are just wanting wireless connections between two boards, and they don't have to connect to anything else, then that opens up other possibilities, such as using wifi, or LORA radio. If you need to interact with the boards from a smart phone using some sort of app to do basic things that might be doable. If you need the Teensys to act as bluetooth midi controllers, then it maybe harder to find a solution, as you might need BLE boards that present the midi interface.
Adafruit has 2 boards that do BLE, one that uses SPI and the other serial UART. I'm sure there are other boards that would work as well, particularly if you would connect to it via a serial UART:
In terms of UART, the Adafruit page says it requires CTS/RTS support. Note, the Teensy LC does not support CTS/RTS. I'm not sure the Teensy 4.0 supports it either as the Serial page has not been updated for Teensy 4.0. The Teensy 3.2, 3.5, and 3.6 support RTS/CTS using certain pins for CTS (RTS can be any pin):
That means the SPI version is probably better for the bluetooth end of things. SPI is often used for displays, and sometimes SPI devices don't work too well when they are sharing a SPI bus.