It's an LLC. We have a lawyer as a member of the group, so he drafted our purchase and sale agreement and our operating agreement. We had to hire a local lawyer, too, to draft an affidavit and to register the deed.
If you're willing to share, I (and I'm sure others here as well) would be curious to get some kind of sense of how you wrote out the agreements.
I'm the lawyer that Tynan mentioned, and the proud part-owner of the island. There are excellent standard form agreements available for free online. Essentially you just search for the relevant jurisdiction (i.e. the State where you're incorporating)and "standard form multiple member LLC operating agreement". Then you edit the agreement to fit your circumstances, deleting and adding as required. Standard form purchase and sale agreements are also easy to find and don't require much amendment. Pay a local title search company to check the title (ensures that there are no outstanding mortgages/covenants on it, that the seller actually owns it etc. You'll need to get a local lawyer to execute the deed, but that doesn't cost much. It helps to have a legal background, but an agreement is just a shared understanding of the meaning of words, so not too difficult.