I don't think you can properly do what you are trying to with your current router (unless you can upgrade it to OpenWRT or equivalent.). Its also A LOT harder to do then you think - and probably can't be done through the web interface alone.

As has already been pointed out, each subnet needs to point to the router with an IP in its own netblock.

Thus on LAN Interface of the router you need to have 2 IP addresses - 192.168.0.1 and 192.168.0.254 (or, in the second case, an Ip address in 192.168.0.129 - 192.168.0.254 which you are not using). In order to do this you need to bind a second IP address to the router, and it does not appear to allow you to do this.

Even if you do achieve the above, you are still only part way to your goals. If you are using DHCP, you need to have the DHCP server answer on both subnets, and provide IP's in the appropriate range for each subnet. Again, this is doable but probably not with your current router.

The question to ask though is "Why are you doing this". Doing this does not buy you any significant security/isolation because the systems are still on the same segment, ie computers in one half can read and respond to broadcast traffic in the other half. The typical way of handling this problem is thus a bit more complex - and again, you need more powerful router software to pull it off. (In order to fully understand what I'm going on about here, you need to understand the difference between a subnet and network segment - the 2 concepts go hand-in-hand, and generally 1 subnet=1 segment, but you are describing 2 subnets on 1 segment - which is often not what you want)

The way I have done something similar is thus - I got a router which supported OpenWRT. I configured the LAN ports on the router into different VLANS. (Most 4 port routers are interesting in as much as the 4 lan ports are actually individually accessed, and the software makes them appear as a switch and interchangeable - but you can actually program them to be on different VLANS, and provide per-port isolation). You then put each VLAN in a different subnet, and assign an IP address to the router interface for each subnet. You will probably need 2 switches (if you have more then 3 devices in any subnet) - you would need to use 1 of the switches for each subnet. In this way computers are in different network segments and - from a practical POV - can't talk to each other without going through the router. [ That said, I can point you to articles which say don't rely on VLANS for security - although I don't agree with their conclusions ]

The first basic thing you can do is bring up a commmand window as well as browsers for your individual router admin page. When say you know the IP address of PC1 by typing ipconfig into the CMD window you can see your IP address, and needless to say this needs to be on the same network range as all your other devices (routers and PC2) to see them unless you know how to setup that connection on the routers to "Route" from one network range to another.

This is for if the router2 is connected to router1 through the LAN ports on both machines.

most of your internal devices I would say are on the 192.168.1.0 range.
As a possible solution have the Router connected to the internet setup for DHCP with an IP address of 192.168.1.1 and a subnet of 255.255.255.0 . Check PC1 is connected with that address as the default route in the CMD window with ipconfig. Next in the admin page for router2 make sure it has the default route setup as 192.168.1.1 with its IP as 192.168.1.2. Lastly in PC2 you can try and type Ping to all three of those IP addressses to see if it completes successfully.

After all that is done and you still have issues it may be because you need to type a double \ at the beginning of the url PC2\MySharedFolder

I would like to clarify my solution is to put everything on the same network IP/subnet mask range, because I believe that is the only way Windows workgroup sharing will actuall work; but I may be wrong on that.