Thalia is displaying the group Corybantes correctly as her offspring, possibly due to not having any additional offspring entries, but in Apollo's case the code for the group seems to be in conflict with the single value code representing his other offspring.

This disparity seems to be evident if you click on the character entry for Hector: the final two sibling entries display out of order as "Telestas. Troilus," (Troilus being a child of Apollo). After discussing it with Greg, the code seems to be correct but requires additional tweaking.

Edited to Add: This problem does not appear to be unique to Apollo. Agenor_10, archelochus, acamas_2, theano, glaucus_5, coon, helicaon, iphidamas, laodocus_2, polybus_3, aeneas, hermes, abderus, autolycus_2, cephalus_3, eleusis, eurytus_2, myrtilus, and pan are exhibiting the same display issue. There is no "groups.xml#whatever" to compete with the existing code for these characters, so the display issue appears to be unrelated.