appeal to same school as sibling

[relate]

Hi,

Got the results online. My ds did not get his first choice which is KEGS where his older brother is (Year 9). He got the 2nd choice CRGS.

His scores are

31/50 English
33/40 Maths
61/80 VR

Score 345

Ranking 186/740 KEGS
110/493 CRGS

Can I appeal,considering the position in KEGS? What are the procedures?