Dissolution of Private Trust - Taxability of Funds

I have a question regarding Private Trusts and the best way to explain it is with, perhaps, an example:

1)        I (the Settlor) start a Private, Revocable, Trust for the education expenses of my grandchildren and transfer some of my Funds into the Trust.

2)        The Trustees are myself, my spouse, and my son.

3)        The beneficiaries are my 2 grandchildren.

4)        The education expenses are to be met from the Interest / dividend income of the Trust Funds, keeping the capital intact. 

My Question is, once the purpose of the Trust is over, i.e. education of the grandchildren is complete, and it is decided to dissolve the Trust, what will be the Tax treatment in the following cases, IF:

a)         The Trust Funds go back to the Settlor, (if alive)

b)         The Trust Funds go to the Trustee (son)

c)        The Trust Funds go to the beneficiaries (grandchildren)  

Thank you for your guidance.