how many of the students attending here are illegal aliens, or anchor babies who should be illegal aliens?
Students attending in D.C., or students currently attending these Catholic schools?
I don't know the answer but I suspect you could get an approximation by looking at the number of "English language learners" at each school or in the district.
In DC? Probably less than the national average. DC is only about 8% Hispanic, which is less than the 14% national average. Plus, DC has a lot of diplomats and students living here, so that 8% probably includes a couple of percentage points that are not really part of the equation.