Run. What you need to do is full rewrite. You need business owners backing you up on this intention. From your description they don’t understand the scale of t

Run. What you need to do is full rewrite. You need business owners backing you up on this intention. From your description they don’t understand the scale of the problem. So that’s a dead end. When they will understand that they have to halt all new developments for few years and drastically increase budgets for development team meantime, you can start thinking about how to proceed. But they will not.