Being 'Fair' when paying for college cost for several children

Okay, let me first start by saying that we of course know that your cannot treat your children all the same and provide everything equally to them in life.
So, my thread is intended to discuss college cost specifically.

We have several children. 2 are currently in college. Another couple are headed that way soon, then the youngsters will bring up the rear.

For the two in college:
Son1 turned down a full ride and is at an Ivy. Our EFC is, of course, more than we like but we are making it. Son works summers to have spending money, is an RA so that means no room cost and 1/2 of his meal plan is covered. He also took out the fed. loan years 1 and 2, may not need to years 3 and 4. He is doing his share to help. He really wanted this school, (well, really wanted an Ivy) and agreed to pull his weight to make it happen. He is happy with his choice.

Daugh1 took a full ride and turned down an Ivy and some top LACs. She too is very happy at her school and likes not being in an academic pressure cooker. However, she has to keep a high GPA to keep her scholarship and stay in her honors program. This includes also volunteer work. She does not hold a campus job. We send her spending money (small amount) each month. She also has traveled each summer, abroad (and won partial scholarships to do so), and has done internships (unpaid). She is doing her share with keeping her full ride by great academic performance, school involvement and volunteering…

Even with the summer travels and spending money, we are spending only a small fraction on D1 compared to Son1. We now are wondering if $ we put aside for Daug. should go to her towards graduate school or whatever she wants upon graduation, or be saved for younger siblings (or put toward oldest son to ensure he need not take out any additional loans)?

What do you all do if you are spending way more on one child than the other(s)?

We cannot see the future, but the next up is actively working toward a full ride and I think will be able to get one (or at least full tuition), somewhere. He sees his sister’s life as way better than his brother’s (financial freedom from loans, extra jobs, etc). Going to a ‘named’ school is not relevant to him. He also would be totally content at a state school. 4th struggles in school a great deal, but is mr. fix it. He is thinking community college for a trade, maybe the military. Younger ones? I have no idea. By then, I will likely hand over the college confidential site and tell them ‘best of luck with whatever you choose’!

There is already a thread discussing the exact same thing:

http://talk.collegeconfidential.com/parents-forum/1891666-considering-fairness-when-paying-sibling-college-costs-p1.html