The principal said that since father has given wife POA she is allowed to make changes and that in the court order it doesnt say what days I am suppose to pick them up nor how i am suppose to pick them up. And I cant add myself back on the list because I do not have sole physical custody
Apparently principal is ignoring the fact that you have joint LEGAL custody.
1) I would ask that the principal verify her stance
in writing. Because rankly, it sounds so crazy that a judge might not believe it otherwise, should you feel the need to bring it up in court in the future. Most schools/school districts try to stay out of the fray, and only block a parent when there is
documentation that the parent is only to have supervised visitation or there's a restraining order.
2) Call and send a letter to the superintendent of schools and the school board. How stern you want to be is up to you. However, since you have already met with the principal, it would not be unreasonable to request that your parental rights and your LEGAL joint custody be acknowledged, and that you be provided full access to YOUR LEGAL children, school communications, and school records (<- bet you're not getting a copy of their report cards), and that failure to recognize your legal rights as a LEGAL parent with joint legal custody of your children in the future will result in legal action against the school district.