how should i format the xaxes crosshair label?

The second label is a tooltip header, to disable it set:

    tooltip: {
        headerFormat: ''
    }

As to your second question: strings in your data format are treated as point names, so instead of:

data: [
  ['1', 1],
  ...
]

Set:

data: [
  [1, 1],
  ...
]

Live demo: https://jsfiddle.net/BlackLabel/1g4m2ka8/

API Reference: https://api.highcharts.com/highstock/tooltip.headerFormat