Solaris 8: Multiple primary interfaces connected to the same network

Question

I have a machine with Solaris 8, and it has multiple interfaces that are connected to the same network which means they all have metric 0 (1 hop) to the default gateway.
assume:
e1000g0: 192.168.30.70
e1000g2: 192.168.30.72
e1000g4: 192.168.30.74
e1000g5: 192.168.30.76
gateway: 192.168.30.65 (Cisco Router)
However, it seems like despite the fact that they have a direct connection, they seem to be using e1000g0 to access the 192.168.30.0 network to get to the default gateway and then to anywhere else.
When I send a ping to say, 192.168.30.74 (IP of e1000g4) and capture packets on e1000g0, I see the "echo reply" messages going out of it as opposed to e1000g4 even though e1000g4 is the one receiving the "echo request". This should not happen and these should be completely independent as they should all be advertising a 1 hop to that network
The outputs from netstat -rn and ifconfig -a are shown in the picture on the link below
[http://img836.imageshack.us/img836/7308/ifconfignetstathiddenip.jpg]
This gets even more confusing when I go into the Cisco router and run the command: "show mac address-table" where only the MAC address of e1000g0 is shown for the switch port it's connected to, but not for the other interfaces which are connected to the switch. Yes, all ports are active (no shut) and are pingable.
Also, the odd thing is that ALL of these individual MACs show up in the router ARP table when the machine comes up, however after sending a ping to one of them, after a certain expiry or whatever period, the MACs disappear from the router ARP table and only the MAC for e1000g0 shows up. The arp table of the solaris machine however shows all the relevant MACs of each port of the router that it's physically connected to (This is actually a Cisco Switch with the advanced IP services imagine and L3 routing turned on)
Before anyone asks: The setting local-mac-address? setting does NOT exist in my machine and it never has, but it used to work fine. Also, from the ifconfig command, once can tell that all the MAC addresses are fine.
I need to somehow assign all these interfaces equal priority and make them understand that they're physically connected to the 192.168.30.0 network and there's no need to go through e1000g0 to get to it.
This is causing a lot of problems as eventually all traffic will end up going through the e1000g0 interface and that will become a bottle neck.
Please help Thanks in advance

Answer 1

Ok thanks. That was a useful response.
I did think about the trunking software that is claimed to be available for Solaris 8, but it's only available if you've got paid support contract. Oracle came and ruined everything re: Sun support which is so expensive now.
The other confusion is, we never had that OR needed to configure trunking/link aggregation on this machine, so why now?
Lastly, by your explanation, this should be expected and is "normal" behaviour, which would mean that this machine was always doing this and I only just noticed it this time? I thought if you turn off ipv4 forwarding and router function in the machine, it's every interface for itself. But it's not doing that :(
So then the question is, Can I force it? I've tried a bunch of things by manipulating the tables and it seems to mess things up where nothing is getting through or it now shifts all the traffic to some other port make the problem no different
Is there a way to give equal weight to all interfaces for the traffic to go directly through them that is originating at those ports?