It sounds like you are relatively new to being a tech lead, so I write this comment with that assumption.
This team really needs a manager. Someone who can take responsibility for the problem, someone who has the power to fire and hire if need be. And someone who can mentor new tech leads like you. Who can help them with the communication and persuasion parts of the job. It sounds like there is no such person here.
It's not a great situation for you. The ideal time to start being a tech lead is with a group who trusts you, or with management who can help you gain this trust. You don't have either of these things.
This team also sounds like it's a low priority for management. They don't want huge outages, sure, but it hasn't been worth management taking a very active interest for the past couple years.
So, basically, it's just not a great situation. It's certainly possible to stick with it, and if you do, I suggest being more focused. Just deal with the outages, don't expect to be able to put best practices into place very quickly. Especially since this team sounds like it has been accumulating low performers over time.
This team really needs a manager. Someone who can take responsibility for the problem, someone who has the power to fire and hire if need be. And someone who can mentor new tech leads like you. Who can help them with the communication and persuasion parts of the job. It sounds like there is no such person here.
It's not a great situation for you. The ideal time to start being a tech lead is with a group who trusts you, or with management who can help you gain this trust. You don't have either of these things.
This team also sounds like it's a low priority for management. They don't want huge outages, sure, but it hasn't been worth management taking a very active interest for the past couple years.
So, basically, it's just not a great situation. It's certainly possible to stick with it, and if you do, I suggest being more focused. Just deal with the outages, don't expect to be able to put best practices into place very quickly. Especially since this team sounds like it has been accumulating low performers over time.