Did you have any say during the hiring process ? I’ve been in a situation very similar to this. I needed help and management hired a consultant to work as a front-end developer. I needed someone experienced with Angular and that consultant had no experience whatsoever.
You’re not letting anybody down and you’re not a horrible tech lead.
First, your team should help you focus on priorities. You can’t be expected to juggle so many balls at once. You have to focus on what matters the most for the company.
Second, hard deadlines are BS. Yes shipping is important but not at the expense of the team’s health.
There are plenty of resources online about how hard deadlines just make things worse.
If I were you, I would sit down with management and make sure they understand my situation and figure out a way to move forward without burning out.
Working 10-11 hours days and weekends is just not sustainable. Believe me I’ve been there. It’s not worth it.
You are not shackled to your job. It took me a while to figure this out. You don’t have to feel bad about yourself just because you’re being asked to handle a ridiculous workload and you’re struggling. I would struggle too in your situation.
If management values your work, they will listen and try improve the work culture. If they don’t care, then it’s time to look elsewhere.
Good luck