Sorry to be here about your job woes bro. Totally different situation but at my job, I work for the State, we are unionized and have "and other duties as seen fit by the Division". This covers exactly the type of work you are being forced into doing. However, signing off on "completed" work for employees that I do not directly supervise does not happen. In New Hampshire, the employer can fire an employee for any reason and then it would be up to agrieved former employee to sue the employer for some type of work related issue. Not a great set up. It doesn't sound like you are a union employee, especially in a pseudo management role. Therefore protection from an irritated boss is not afforded.
My role at my job is a director of a program for the entire State. My title is Trooper First Class. Every other State that has State Police running their program, has a Lieutenant or higher in this place. I am directly responsible for overseeing about 125 companies and enforcing laws and regulations on about 6500 people and 5k pieces of equipment. If something bad happens, I am the program manager. If I were to grieve my position, I would simply be moved to a patrol capacity and another Trooper would fill my role once application and interviews were completed. And it all boils down to that caveat written into every role within the Division and even the Department which oversees the Division. I knew about this going in and still took the job. You're problem is you did not. The job title had changed, the position changed, the responsibilities changed and by tossing you a raise where others didn't get it, they have kind of sweeted you into the job.
Have you spoken with your supervisors about your concerns. To me, this is a concern, you sign off on employees who do work on things that house some pretty precious cargo....humans. You have no authority to hire of fire so presumably take no role as an enforcer of policy or code. That is not a great position to be in. I tell people all of the time, I can be sued thirty years from now because of my role as a trainer when I was a patrol supervisor. I sign off on a guy and he does something stupid way, way down the road...I still own it. Back then I had the authority to do something about a bad employee but you don't. That's an issue. I know this doesn't help but at the end of this tirade....you have a girl friend, you're young, you're skilled, you have a long life ahead of you. Don't forget that. I would make sure I have something else lined up, and talk to your boss. I tell new guys on the job this. It sounds like a dick thing to say, but it's true....
"ALWAYS put your family first. This job will forget you the day you walk out that door". A former Patrol Lieutenant told me this when I was a rookie cop.
I know we have different t jobs but life is life. Family first. If you feel, and you certainly do, and rightly so, that you are being treated unfairly at your job, speak up. But....try to have something else lined up. Maybe closer to home. I'd rather wake up to my wife than an empty pillow miles from home at a job I don't like that has caused me frustration and stress.
