I am CanadXXXXX XXXXXve in the US. My x-wife is an America living…

I am CanadXXXXX XXXXXve in the US. My x-wife is an America living in Canada as a PR.   We have shared legal custody and she has full physical custody of our 3 children.   I tried for a number of years to have my x register them with the US consulate in Canada so they can acquire their US Citizenship, she never did. In 2007 my oldest was living with me so I spent time and money and managed to get his US passport (easiest and cheapest way to obtain citizenship within the US). Mind you it took a lot of effort to have his mother sign the passport app.. then this summer while I had the other two child as well, I managed to get their passports done, and again my x drag her heels about this. Anyway now my sons are back to Canada. In the past my x has lost documents (Birth Certs, travel docs etc..) so I really do not want to give her all three passport which cost me over 600USD. However I want the document to be in Canada, so the question is: Can I legally have my father (who is in Canada, same province) be appointed the holder of the passport in lue of me while my sons are under the age of 16 or 18 whatever the legal age is in Nova Scotia?

Perhaps it sounds petty, but, she all of a sudden "NEEDS" these documents she really didn't want to help obtain!!! She even threatened me that she will send the police to my parents place to get them... Mind you I never told her she could not have them, I just told her I left them with my dad, and I would prefer they stayed with him unless she or my parents or any other family member needed them to travel with my/our sons.

thanks...