If guardianship is obtained in Mexico where my parents live, will it cover accounts still held in the US?

Both parents have dementia and are becoming more demented and combative by the day. I need to more to apply for guardianship before long. I am afraid one may end up killing the other if left to their own devices. My question is since they live and have citizenship in Mexico, if guardianship is obtained there will it cover their finances and accounts still held in the US?
PS they refuse to return to the US even if it were possible.