Bind IP address for S2S

Hi to all.
I have a computer PC1 with ejabberd and 2 network interface on board.
The IP address of network interfaces are: 10.11.9.1 (eth0) and 10.11.4.29 (eth1).
Then I have 2 virtual host on ejabberd, called: warning and alarm and I have 2 user, one is logged on warning (user1@warning) and one is logged on alarm (user2@alarm).

Then I have another computer PC2 with ejabberd and 1 network interface with IP address: 10.11.7.1 (eth0); on this server (called autotreno) I have an user logged: user3@autotreno.

Between PC1 and PC2 I have a router with 3 network interfaces. The plan is this:

user2
10.11.9.1 <----------> 10.11.9.12

_________________________________________user3
_________________10.11.7.12 <-------------> (10.11.7.1)

user1
10.11.4.29 <--------> 10.11.4.12

PC1_______________router_________________PC2

I have done 2 connection S2S, one PC1<--->PC3 and one PC2<--->PC3.

Now, what I want is bind IP address for each virtual host on PC1:
10.11.4.29 <-> warning
10.11.9.1 <-> alarm

(in file /etc/hosts I have already done this mapping)

I want this because packets that I send from user1 must have IP 10.11.4.29 and packets that I send from user2 must have IP 10.11.9.1. Instead, now, if I do sniffing on router, I see that the packets from user1 and user2 have all same IP 10.11.9.1 (or same IP 10.11.4.29).

I have already done this:
{ip, {10, 11, 4, 29}}.
on configuration file (at voice Listening Ports) but it don't solve my problem.

Do you understand my problem?
I hope yes.
Thank you to all in advance.
Crystal