Share a Message Review with your attorney
From a Message Review, choose Share with your attorney and enter their email address. On the Free tier they get the same 3-incident sample that goes to your phone; on either paid plan they get the full Message Review.
They get an invitation at that address. To open it they install the free CustodyComms iPhone app and sign in with that same address: the invitation is tied to the address you sent it to, so it will not open for anyone else. There is nothing for them to buy.
You can share with up to 10 people on one Message Review, and you can remove any of them later from your account's Shares page. Removing someone stops their access from that point; it cannot pull back a copy they have already opened.