I have two sip clients. Client1 registers to kamailio1, Client2 registers to kamailio2. Kamailio1 and kamalio2 sharing one database. I want to make call between client1 and client2. What should I do?

Another question is that I want to achieve load balancing with kamailios.

The architecture is described as: I run one kamailio instance as load balancer, other to help make calls, and the load balancer dispatchs requests to other kamailios. 

So, how should I do that? Has anyone ever achieved this? Give me a hand, thanks very much.