As an accountant I've handled lots of contracts. I do not think those questions constitute a legally enforceable contract, no matter what the watchtower's lawyers say.
Problems
1) Mutual consent. Witnesses could make a good case they entered into the contract under duress. Certainly a child cannot enter a contract.
2) Consideration. There needs to be a mutual exchange of value between the two parties. You agree to sell me your car for a hundred dollars. I get a car you get $100. What does the R&F Witness get for selling his soul to the publishing company?
3) Capacity. A person has to understand what they are entering into. See my comment about duress. They also ensnare people who are in the midst of some sort of crisis. This can void a contract.
4) Legality. You can't contract to do something illegal, like say withhold information about CSA in you congregation.
Obviously the WTBS uses this talk about a contract to flog their membership into compliance. Where is a copy of this contract, with signatures and all that? A contract doesn't have to be in writing, but if it isn't how do you prove what it says?