3-4 years out is a long time in college admissions and financial aid. Schools have no idea what their policies might be then. Even if they say something now, there’s no assurance that will still be the case a few years out. Not only are practices and policies dynamic, but there is so much turnover in admissions and FA personnel each year…and new peeps often change things. Maybe some grandfather current students in, while some won’t. Not much you can do beyond what you already are.
I don’t think any of us can predict which profile schools might still consider sibling college expenses and which won’t 3-4 years down the road. They are faced with advantaging families who had their kids close together, a benefit those with kids farther apart can’t access…Reasonable people fall on both sides of the issue.