Motorbikes are family vehicles in Jakarta. Three on a motorbike (two adults and a child) is common. Four is a bit more unusual. I've only seen five a handful of times.
There are more motorbikes than cars on the road in Jakarta, and the number is growing by leaps and bounds. That's partly because traffic rules, to the extent that they exist, are generally viewed as optional for bikes, so the drivers weave in and out of lanes and up onto the sidewalks to get around the city's notorious traffic jams.