Is seelkadoom sonics brother

No. Well it is not proven that Sonic did have any other siblings besides Sonia and Manic who were later on discarded by the Sonic team along with Sally Alicia Acorn, Antoine,and that walrus guy plus a number of robots including the chicken guy and his friend who were later on edited on to Deco and Boco (Sonic X) who were edited on to this crazy light bulb guy(Sonic Unleashed).