Can I delete only 2 of the 12 1099's I received from one broker or must I delete all 12?

Yes, you can delete 2 of the 12 Form 1099's entered in individually (from your broker) as needed. You can also edit and add as desired for any all Form 1099-INT, Form 1099-DIV, Form 1099-OID, and Form 1099-B transactions.

To delete Form 1099-B

1. Sign in to TurboTax
2. Select "Take me to my return"
3. Type "Form 1099-B" in the "Search" 
4. Click on "Jump to 1099-B"
5. Select "Yes" on the "Did you sell any investments in 2017?" screen
6. Click "Edit" on the "Here's the investment sales info we have so far" screen to edit.

OR

     7.  Select "Delete" next to the transaction(s) you want to remove from TurboTax.