Regarding the "leverage", neglecting to have you sign an IP transfer agreement would be a major oversight by the founders and a potential red flag.
I wonder how many founders are there and their roles? Are they fulltime? Is there a CTO? Or are the two contracted developers fully in charge of the product? It then comes down to what role you're looking for in the company, beyond being a contractor.
Also, how are they currently funded? Are they about to raise a seed round? You suggest your stock "options" aren't worth much. However, if the company is brand new and you're paid less than a market salary, then it's possible that owning substantial stock would be appropriate.