How much equity in your house? I’d use that!
It sounds like you haven’t filled out the CSS Profile. Pay attention to the special circumstances section, if there are any. Having three more kids on the way to college (and needing support like food, right now!) might help. Health issues, family responsibilities, change in job , that kind of thing can all help.
Ivies determine their aid and don’t negotiate for the most part though as one poster said, they might rerun the numbers if, say, Princeton offers more. But Harvard is very generous.
Some families do get some aid with incomes above $150k. I would do the full application for aid and then talk with admissions folks, either in person or on the phone. They welcome this. I told one Ivy FA I didn’t want my kid to get excited about attending until I had spoken with them.
Harvard doesn’t include loans in their financial aid package, as you no doubt know. But you could finance this if you wanted. The problem is that you have three more to pay college for. You may have to be fair (a family decision) so you have to think about cost times 4, as it seems you are.
Now that your son got into Harvard, it is hard not to send him, right? That’s the problem! Our state university now has a lot of students whose family could not pay for the Ivy they got into. But it is tough if your kid is one who will always think about how he got in and didn’t go. Some personalities don’t hold onto this and move on in a healthy way though.