Re: your business, it may not matter if you have a contract with these jokers or not.
If you are in the US, there is something called the Uniform Partnership Act, which acts as a backdrop to many partnership transactions, even if not written down contractually between the partners. (See
http://en.wikipedia.org/wiki/Uniform_Partnership_Act)
Look it up for your state, and see what is and isn't covered. (Or see an attorney for this, but this will help you know what to ask.)
It is very possible that you guys did everything informally and that this act will provide for certain standard terms even if not written down. (Example: so they cannot take 13% for you.) It might not, and it all depends, but it is something to look at.