Kim Zolciak's 3 Younger Kids Challenge Decision in Brother KJ's Sex Case

Kim Zolciak's son KJ Biermann's sexual battery case is turning into a family affair ... with three of his younger siblings now entering the legal battle.

According to a Page Six report, the Georgia Court of Appeals granted the children's request Thursday to challenge a lower court ruling connected to their 15-year-old brother's ongoing criminal case.

The siblings, represented by attorney Darice Marie Good, initially filed their request October 23 ... and their lawyer filed a notice of appeal Thursday after getting the green light.

It's unclear exactly which ruling the siblings are challenging or why they're involved in the case ... and the appeals court's decision doesn't mean the original ruling has been overturned.

As TMZ previously reported ... KJ was arrested in August after a female classmate accused him of sexually assaulting her inside a Georgia gym. He was later indicted on seven felony charges, including aggravated sexual battery and aggravated sodomy.

KJ has pleaded not guilty to all seven charges ... and his attorneys have since challenged the indictment, arguing prosecutors haven't provided enough details to support key elements of the allegations.