You would 'lock' these form fields since editing directly in tables is not kosher. If that's what you're doing, there is no way to lock fields at the table level.
I don't understand your second question. "Locking" fields has something to do with eliminating tables? Unless a vendor or employee can have more than one address, I don't see why you'd have separate tables for their addresses.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.