This is such a complex issue. I can see both sides of it, even though my perspective is that of a SM.
For example, I could ask that if you were not going to reconcile with your H and met someone new that was spending $500/mo on his daughter, would you expect him to stop because his money would suddenly become marital money? I think probably not, because you would recognize that you might not have a leg to stand on. But that's different.
I think the real key in your sitch is that this is not a NEW M. You've been M'd for 15 years, which means you spent a good portion of your M, and I'm sure your personal finances, on your steps when they were younger. When people hear your sitch *now* and your approach to things *now*, I don't think that's being taken into consideration. So if splitting things up by percentages were a viable option, then it should have been done years ago when it was 1 of you vs. 4 of them. Your H should have been paying 80% of everything. I didn't get that impression from your earlier posts, but rather that your income was used to supplement his shortfall. I also got the impression that you were previously very generous, but simply feel now like enough is enough.
There really isn't a correct answer, or a right or wrong. It really boils down to what works for you, and I don't think there's anything wrong with defining your personal hill.
