FAFSA for two kids resulted in two different EFC numbers. Huh?

Are they twins? Or are they born in different years? Are they in the same year in school? Not sure if the FAFSA result gets affected by whether one student is a different year in school than another (in the same family) - freshman vs. junior - for example. Some colleges seem to adjust for that in their calculations as they assume the same student in a higher year in school should be able to contribute more…usually it is a summer earnings implicit assumption.