1) For a contract to be enforceable, it needs to show offer, acceptance, and consideration (basically, payment). If one party creates a contract and sends it to the other, then the other party signs it as is and returns it, that's enough to create an enforceable contract--they extended an offer (by creating and sending you the contract) and you accepted it (by signing). Since they created the contract and sent it to you, your signature makes it operative; they did not need to also sign it.2) An enforcable contract is enforceable against either/both parties, so if they contracted to produce 2 videos but only produced one, you may have grounds for legal action against them.