Sounds like there's a BB30 to threaded BSA sleeve that was pressed in with a hammer by an amateur.
With the BB30 frame, there are a host of better options for bottoms brackets than a pressed-in sleeve with threaded cups. Here are some that thread together (so they don't creak) and would fit 24mm FSA or Shimano BB spindles:
Praxis Works Conv BB
https://praxiscycles.com/product/shimano-conversion-bb/
Wheels Mfg BB30-OUT
BB30 Outboard Angular Contact BB for 24mm Cranks (Shimano) - Black
Wishbone BB3024
Wishbone enterprise co Ltd, Product:: Bottom Bracket, BB Parts, Pulley Wheel, Jockey Wheel, Wheel Bearings, Crankset, Chainring
Token Ninja
https://www.tokenproducts.com/bottom...bottom-bracket
Alternatively, you could source some BB30 cranks for the back of the tandem. You'd be stuck with press-in bottom brackets, but they'd be used as intended, which has a certain elegance to it. For traditional crossover drive, you'd need to piece together the crankset and get the left arm pedal threads repaired. SRAM BB30 crankarms and Cannondale SISL2 are good candidates, using a Cannodale SISL2 spindle (121mm for SRAM, 119mm for Cannondale for proper spacing with 145mm rear hubs and double chainrings -- 5-10mm longer spindle for triple chainrings). You'd use two right crankarms. The left would have to get a threaded insert to switch the thread direction (most established bike shops should be able to do this for you). Since the modified crankarm must be aluminum, it narrows your options down to SRAM Rival, older SRAM S350 (Apex), Cannondale SISL2, and Cannondale SISL2 Hollowgram.
We're using a Rival BB30 crankset on our tandem with a BB386 shell. It's been creak-free and pretty awesome so far.