She clearly had no right to do that. It is parental abduction.
So you don't register the order as it is already an order in Ontario. Rather you go do the courthouse in the morning tomorrow. You say you just learned that the mother has taken off with the kids and moved them to Quebec city and this is a clear case of parental abduction and you need to see a Judge on an emergency basis.
The clerk will speak to a Judge and who will likely agree to hear from you.
You then say you are self-representing, the interim order is with the court, but you just learned she moved the children and has enrolled them in school etc and that you want an interim order for sole custody that is police enforceable.
Then you will be able to enlist the assistance of the police to bring the children home.
After that there will be another hearing with the court where then the mother can argue why moving the kids is in their best interests and you will oppose that of course.
I cannot answer about the house on this post. When we are done here you can rate me and start a new post about the house and I am happy to help with that too. I am a senior family lawyer in Ontario.
Please feel free to post back with any follow-up questions you may have. If you don't have any then I hope I have earned a 5 star rating but if you don't feel that I have please don't hesitate to reply back and let me know what more I can do to assist you. Finally, please know that even after you rate me I will be here for you and you can ask follow-up questions if you think of them later on at no further charge of course.