Accepted answer

You need to define yAxis order to keep those series horizontally below each other.

define yAxis:0 ,1,2 and put series in same order as that of yAxis.

yAxis: [ 
        opposite : false,
        min: 0,
        top: 0,
        height: '31%',
        offset: 0   
       } //and so on 

See a working example here

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