Pega Application is a Java application with high memory requirements. You can maintain multiple JVMs in a single linux box, provided you have enough memory for all the JVMs, please refer the link below which provides information on the best practices to configure a JVM.
Adding to the above-suggested solutions, In case if you are using any external load balancer like F5, you can use NATing to assigned different IP addresses to each node. Read more about NATing in the following article.
Note: - While doing the NATing, try all the IPs should be in the same network otherwise you might face some issue with Full-Text search and other HA features in case of network issues whilst application try to join the cluster.