Guardian is for children, Trustee is for money

If you die with underaged children, you need
(1) trustee to look after the money and
(2) the guardian to look after the kid, and the last
(3) the administrator takes care of money operation.

Guardian: guardian is only valid for the children. Guardian decides what time children go to bed, if children need major medical operation, guardian has to consent. Guardian can move children from school to school, etc etc. Guardian are legal parents.

However, anyone (including trustee, neighbor etc) can file a suit in court on behalf of your children against guardian if they found something fishy, just like school teacher can report your child abuse if you hit your kids.  After court proceeding, the court could reappoint other guardians.  

As long as guardian feed the kids and keep them clean, nothing can be done if kids doing poorly in school because those are not necessity of living.  So pick your guardian carefully if you want your kids go to ivy leagues after you die. 

Administrator: usually a bank or a lawyer, it takes care of paperwork, such as monthly check to the guardian for child care needs, occasional request from guardian for medical expense etc.

Trustee: Trustee make deicision on how to manage the money. If you have $1 mil, trustee manages how to invest it, which stock to buy, etc.

Ideally all these people are different so they can check/balance each other. You don't want one person doing all three jobs.

Guardian has to be one person or one couple. Administrator is just a bank. You should appoint as much trustee as you can find, so at least one person is honest enough to call the police (breach of duty) if other trustees are abusing power. Also, trustees make decision by voting, so you want odd number of trustees.

Yes, ideally trustees be living in US so that US law can reach them. Otherwise, who is stopping trustees to move money offshore to China? Your kids are in US their lawyer would have difficulties recover money from China.