The copies can be in the same folder with each other.
Right click the EA Land file, select copy, right click an empty spot in the folder, select paste, rename the copy TC3.
Open the folder, find the client.exe and copy them adding "-CSCity:EA Land" to the first one and
"-CSCity:Test Center 3" on the new one, to the target lines. You can send those shortcuts to the desktop for easy access.
If you know how to run multiple sims it is pretty much the same thing.
I am not a techie at all. All I know is to copy the folder, make a shortcut to the client and send it to where you want to go. Fix your shortcuts the way you want them. Click to open one client then the other both windows will go to dif cities. This allows you to play both cities at once, with multiple accounts.
You will only be able to run one sim on each acct at the same time.
When there is an update it is best to open each city with the patch.exe rather than the client. But with the patch you can only run one instance at a time. I run it to patch and then back to the client.