How to consolidate multiple servers for CPU and Memory with Kubernetes
Since Pod is running on single node it can use resources from this node only. And CPU/MEM can't be shared here. At least without special software for distributed computation.
In your case you should consider using ActiveMQ Clustering (https://activemq.apache.org/clustering). In that way you will be able to spread load across multiple k8s nodes with ActiveMQ pods running on them.
So use k8s Deployment + pod affinity to be sure pods will be scheduled to different nodes.