OP has not returned.
However, the problem “how do we handle two kids in college” hasn’t been thought through: Princeton is a meet-need school.
OP, run the NPC with 2 kids in college: doesn’t Princeton offer you some financial aid?
Does it make the situation easier for you?
(Note that there wouldn’t be a difference in FA if your son attends a UC, because you’re not eligible for FA there.)
As others have said, the issue is that you’re only thinking about this now, when you told your son his side of the deal was to work hard and get into Princeton, your side was that you’d pay for it. He worked hard and got into Princeton IN DECEMBER. He’s gotten used to the idea he’s going to Princeton in the past 3 months. You’ve had 3 months to discuss this. So, I feel really bad for your son and of course he’s feeling betrayed, probably angry and flabbergasted.
How long would you have to postpone retirement?
Are the two in college affordable once you’ve done the NPC with 2 in college (who, by the way, may not get into Princeton, and may not want to go to such a college?)
Another issue is that I’d be hesitant to “force” a student to go to a UC, even UCB, when they got into a top private school, in the light of the recently announced cuts. Quality of advising is already terrible at UCB (essentially, students don’t have a personal adviser for 2 years) but think about the effects of the cuts upon teaching, learning, quality of life. I’m sure that kids whose dream school is UCB are thrilled to get in - your son, on the other hand, will not just resent you for a couple weeks, because he’ll constantly be reminded of the difference between a prestigious college where undergraduate conditions have been bled dry due to the cuts, vs.most colleges where learning conditions are good to comfortable. Every time he tries to go to the library and it’s closed, every time he can’t see his TA because there are too many people in his section, every time something breaks in a lab and isn’t replaced. Not being able to graduate in 4 years, a problem that has been averted for years, is likely to return, and with his major so does the likelihood of graduating in 5 years (or more, due to the sequential nature of the program, if you can’t get into a class your path is disturbed.)
Where else has your son been admitted?
Side note: it’s quite possible to visit Princeton and dislike it. But usually when compared to other similar places (kid whose choice was Vassar, Princeton, and Yale, chose Yale and rally dislike Princeton).