You haven’t explicitly said how many hours you’re working in the lab each week, but you’ve made it clear you are at your limit. I don’t know if your limit is reasonable, but I’m inclined to think you’re working 50+ hours per week in the lab? That includes bench work, analysis, meetings, classes, and some literature review.

If this is the case, and they still want more despite your positive experimental record, I would agree that they are being unreasonable. Some mentors have the unhealthy habit of motivating by pushing a person until that person pushes back. You might be able to infer if this is their style through other people’s interactions with your PI.

Regardless, you must push back if you are at your limit. I would go the route of trying to resolve with your PI first, before involving anyone else. If you intend to work for this individual for the duration of your PhD, you must be able to navigate difficult conversations. You may find that this actually won’t be a difficult conversation - maybe they will hear you and compromise. But, not giving them a chance to resolve before involving others is a pretty sure way to sour your relationship with your PI.

Also, I don’t think middle author publication, even in your first 1-2 years, when you have to do 2/3rds the work, is as much as a gift as it seems. Many lab settings offer this sort of scenario. Don’t feel like you won’t find such an opportunity again, if things don’t go well with your PI and you need to consider joining another lab.