How can I protect my ideas when ending a partnership?

I had an idea for an iPhone application, and partnered with a programmer and a designer to implement it two months ago - verbal agreement, they have 50% equity. We're close to launch-ready, but the relationship has been rocky as they won't listen to me. None of us is happy in the partnership, and we all agree launching under these conditions seems imprudent. I'd like to develop my idea with somebody else, or perhaps hire a programmer. The only written agreements are standard NDAs, including non-compete, they signed before I told them my idea. 1) A number of important features and strategies have been added to the original idea over the past two months. They initially suggested some of these ideas, but many of them were formed through our joint discussions. Can I safely use these features in my new company? Does it matter who thought of what during the partnership? 2) How different from the designer's layout and appearance must I deviate to be safe (he's mad, and says I can't use his designs)? 3) Since I brought the original idea, and they signed a non-compete agreement, they aren't allowed to release their code are they? I don't want to compete with them. Thanks for helping me out!