Configure Firehose to read from different Kafka topic Partitions

I am using kafka-firehose to read from a Kafka topic which has 12 partitions. I want to run 2 Realtime nodes such that each node reads from 6 Kafka partitions.
How can I configure Druid to do that?

The kafka firehose uses the high level Kafka consumer, which will handle partition assignment for you if you set up realtime nodes with the same kafka consumerGroup, same druid dataSource, and with druid shardSpecs that have the same type but different partitionNums (start from 0, count up).