Existing businesses have coped with that for hundreds of years.

You can have joint-ventures, where all participants send emissaries to, you can negotiate rights to view the books or other ways to create transparency. You can have contracts, backed by a legal system and state courts.

You can do many things. Blockchains are only one of those possibilities.

Most important question when somebody tries to sell you a blockchain: "What's the traditional way to do it?"

Correct answer: "People usually do X, but our blockchain proposal has advantages Y and Z."

Incorrect answer: "Nobody has ever solved that problem before!"