Sounds like these outcomes are failing:
* Technical Issues Cleared * Deliver on requirements of existing customers * Understand complaints of existing customers * Strengthen relationship with existing customers * Retain talented staff * Strong leadership from leadership team (co-founders)
But these outcomes are succeeding:
* Successful brand awareness in market * Gain initial revenue from customers
So based on this, what outcomes are important? How do you measure their importance? And then what is their role in this? Obviously they're not happy with you either - the put downs, the lack of respect in conversations means there's some unresolved resentment from their end as well.
Personally, I'd recommend both parties write down their concerns, outcomes, and measures, and then with a mediator work through what's important. Contact me if you need a hand.
It's a bit like a marriage - it can be saved, but you both have to acknowledge your 50% in contributing to this situation.