make sure to check this thread, it has detailed explanations: A user's guide to i2c
basically, there are several devices/firmwares that can act as i2c leaders. each one will have different hardware requirements (see the thread above) and might require additional configuration (described in their respective manuals).
(and specifically, you don’t need to use TT as interconnection but you might need something to provide bus power and pullup resistors, the thread above has the details. also, orca and orca’s heart are different firmwares, the former is a follower, the latter is a leader).