Ok, so I have this manager who made me manager, and he hired a guy who couldn't use Git, and forked our private project on his own public repository. He had 10 years of experience, but he basically had 0 since he worked for his family or something along that line. He was really bad, and at some point he was wondering why his changes wasn't getting pushed properly and it was because he was using two different IDE at the same time and he saved on both of them. He got fired.
Then he hired another guy who was equally terrible. He took one month to do a landing page with three big sections, and he wasn't even finished yet. He would constantly tell me to push to staging and I would return his tickets, because for every five items I requested him to correct he would add two more errors and he wouldn't fix one or two of them. He said I was his QA or something along the line and told me to do his job. When I am a senior developer managing him, and he kept telling me to push his fixes when he wouldn't do them correctly. I escalated this to the manager, but he couldn't care less, and didn't do much to help. He probably didn't want to fire him, because he was the one who hired him, and this guy was supposed to be a senior developer. He told me to coach him and I did my best, but certain things cannot be taught. This guy was arguing that something was centered when the element was leaning 30% to the right, and after 10 minutes he couldn't explain to me how I was wrong. I never worked with such bad developers.
Then the guy left and the manager blamed me for being rude. And the example he came up was that I asked him "Do you want me to do it instead? If you can't do it, I will do it." and apparently that was extremely rude. I mean, at what point is it the fault of the "senior developer" who can't do basic tasks and not the guy managing him? I have a lot of tasks to do and on top of that I need to manage him. I need to do devops, sysadmin, frontend and backend and db tasks. I have no experience in two of those fields. That guy couldn't do a basic task. His CV says he has no experience in PHP, and my manager wanted him to do backend PHP tasks and I had to do them instead. I've never seen this before in my life. Is he trying to gaslight me or worse?
I can definitely see that I could have been less rude, but it's impossible when you have so many tasks. I tried to be constructive and took steps so that I manage the next person better, but if he keeps hiring bad people my head is going to explode. What can I do in this situation?