You can't have two TChart objects in the same Canvas. Some of the other TeeChart versions have the SubChart tool that allows you to do this but this is not implemented in TeeChart Javascript.
In Teechart Javascript you have two alternatives to achieve almost the same:
Have different TChart objects. See the example here.
Have a TChart with multiple Custom axes. See the example here. In this one, note you are manually setting the positions of the axes, so if you want you can separate the different vertical axes in the left side. And also note in this example there's just an horizontal axis, but you can also create several in the same way the vertical axes are created.