I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear about your situation.
The fact that these defendants believe you owe them money has nothing to do with whether the three of you owe the lawyer money. That's not a defense to the issues that are being decided in this particular case. When three people all agree to do something, they are jointly and severally liable - all three of you have the obligation to ensure that the bill is paid. Any disputes between the three of you regarding who owes what are legally irrelevant.
If you were being sued in NY Supreme Court (the rather oddly named trial court) rather than Small Claims, the other defendants would have the ability to file a cross-complaint against you for the money they think you owe them, IF it's related to the fee dispute. And then you'd be able to file an Answer and Counterclaim against them. But that type of motion practice is beyond Small Claims, which tends to be very simplified.
You should also be aware that if the lawyer gets a judgment against all three of you, he's free to collect against whoever he likes, even if you already paid 1/3. But if he decides to take the rest of the bill from you, you'll be able to sue the other 2 parties for their contributions, as long as you agreed that the three of you would split the bill originally. You can also raise any other claims you have against them at that time, and they'll be able to countersue if they think you owe them money for something else.
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