CSS Profile/ Institutional Methodology schools will take into account other siblings enrolled in undergraduate institutions (but this is not likely for sibling in professional schools if you mean post-undergrad). It’s in the standard data entry for the Profile, so it wouldn’t be an unusual circumstance.
Whether or not individual schools “fully account” for it in your view, they have the calculations to account for this, so an appeal for professional judgement wouldn’t be bringing new information to the table.
In order to see how much they are accounting for this, you can easily do multiple runs of the NPCs for one school (pro tip: if you log in using your College Board account, you can auto-fill most information for these from a previous run). Just plug in different numbers of siblings to determine the sensitivity of their algorithm and how much of a discount you’d be getting for each. Since this is a straightforward calculation, I wouldn’t expect that there would be significant differences between these NPC estimates of your discount for siblings and what would be in the actual FA award (unlike some items that would be worth further inquiry, such as home equity vs income).