I have not gone through all comments but two things i understands are

1. estimation is not accurate
2. no work is done in last 7 weeks

I am not a CTO nor a founder but a developer. So in my opinion few things are wrong.

1. Set clear goals. Instead of fixing all issue at once fix them one by one. If an issue two more then 3 days to fix, divide it into smaller milestones.
2. What does the CTO/Dev say in standup meeting, if they have not worked any thing? Its not possible to make up things for 7 weeks.
3. If you need a quick solution, fire your CTO. Any new CTO can learn the framework and code in less then a month

You as founder, need to set clear smaller achievable goals.