I am so sorry to hear your story. It sounds terrible. My advice to you is that you really need an attorney. I know that attorneys are expensive, but it sounds like it may be well worth it considering the heartache you have endured. Some attorneys will work with you on the cost, but it sounds like you have a very serious situation on your hands. My overall assessment is that IF you get an attorney, you can probably fix this, however, it would be very hard to do on your own.
I agree that you should hire an attorney in this situation especially since you are now wanting to move to Texas. The order in Minnesota remains as is until it is modified, which means that if you were to move to Texas the grandparents would still have their right to visitation. If you made it impossible for them to have their visitation (by moving to Texas), you would be in violation of the order. So, you need get the current order modified before you move to Texas.
In order to properly answer your other questions, an attorney would need to review your case in more depth than is possible on a public forum like this one.
This response if for informational purposes only and is not creating a attorney-client relationship. An attorney client relationship only occurs after a retainer has been signed.