I managed to set the x and y axes separately for the line graph.
It was not possible to install separate axes for QCandlestickSeries.

I need to do two things:
1. Set separate axes for Candlestickseries to adjust parameter axisX.setTickCount()
2. Display the x-axis converted datetime to string, instead of indexes

P.S. At least the example on the line graph from my second(2) question will do.

Qt Code: 
  1. from PyQt5 import QtCore, QtGui, QtWidgets, QtChart
  2. from PyQt5.QtCore import Qt
  3. from PyQt5.QtChart import *
  4. import math
  5. import numpy as np
  6. import pandas as pd
  7.  
  8. df = pd.read_csv('file.txt',
  9.                  index_col='DATE',
  10.                  parse_dates=True,
  11.                  infer_datetime_format=True)
  12.  
  13. date = df.iloc[:, 0].index.date
  14. o = df.iloc[:, 0].values
  15. h = df.iloc[:, 1].values
  16. l = df.iloc[:, 2].values
  17. z = df.iloc[:, 3].values
  18. x = len(z)
  19. x_ = x - 1
  20.  
  21. qt = [None] * x
  22. for i in range(0, x):
  23.    qt[i] = (date[i].strftime("%Y/%m/%d"))
  24.  
  25. class MainWindow(QtWidgets.QMainWindow):
  26.     def __init__(self, parent=None):
  27.         super().__init__(parent)
  28.  
  29.         self.step = 30
  30.         self._chart_view = QtChart.QChartView()
  31.         self.scrollbar = QtWidgets.QScrollBar(
  32.             QtCore.Qt.Horizontal,
  33.             sliderMoved=self.onAxisSliderMoved,
  34.             pageStep=self.step,
  35.         )
  36.  
  37.         self.scrollbar.setRange(0, x_)
  38.  
  39.         central_widget = QtWidgets.QWidget()
  40.         self.setCentralWidget(central_widget)
  41.  
  42.         lay = QtWidgets.QVBoxLayout(central_widget)
  43.         for w in (self._chart_view, self.scrollbar):
  44.             lay.addWidget(w)
  45.  
  46.         self._chart = QtChart.QChart()
  47.         self._line_serie = QtChart.QLineSeries()
  48.  
  49.         for i in range(0, len(z)):
  50.             c_ = z[i]
  51.             self._line_serie.append(QtCore.QPointF(i, c_))
  52.  
  53.         min_x, max_x = 0, x_
  54.         self._chart.addSeries(self._line_serie)
  55.  
  56.         axisX = QValueAxis()
  57.         axisX.setTickCount(5)
  58.         axisX.setLabelFormat("%d")
  59.         self._chart.addAxis(axisX, Qt.AlignBottom)
  60.         self._line_serie.attachAxis(axisX)
  61.  
  62.         axisY = QValueAxis()
  63.         #axisY.setLabelFormat("%f")
  64.         self._chart.addAxis(axisY, Qt.AlignLeft)
  65.         self._line_serie.attachAxis(axisY)
  66.  
  67.         self._chart.legend().hide()
  68.         self._chart_view.setChart(self._chart)
  69.         self.lims = np.array([min_x, max_x])
  70.         self.onAxisSliderMoved(self.scrollbar.value())
  71.         self.adjust_axes(1, 31)
  72.  
  73.     def adjust_axes(self, value_min, value_max):
  74.         if value_min > 0 and value_max > 0 and value_max <= x_ and value_max > value_min:
  75.             self._chart.axisX(self._line_serie).setRange(value_min, value_max)
  76.  
  77.     @QtCore.pyqtSlot(int)
  78.     def onAxisSliderMoved(self, value):
  79.         value2 = value + self.step
  80.         value1 = value
  81.         if value2 >= x_:
  82.             value2 = x_
  83.             value1 = value2 - self.step
  84.         self.adjust_axes(math.floor(value1), math.ceil(value2))
  85.  
  86.  
  87. if __name__ == "__main__":
  88.     import sys
  89.  
  90.     app = QtWidgets.QApplication(sys.argv)
  91.     w = MainWindow()
  92.     w.show()
  93.     sys.exit(app.exec_())
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