Pyqt5: How to set the size of layout in QStackedLayout or QStackedWidget

Question

I am pretty new to pyqt5.

I have a question regarding qstacklayout. It might be the same question as the How to make different pages of a QStackedWidget of different sizes? Let's assume that I have done this as below

class MainUI(QDialog)
    def __init__(self, parent=None):
       super().__init__(parent)
       self.initUI()
    
    def initUI(self):
       self.scroll_area=QScrollArea()
       self.main_layout=QHBoxLayout()
       self.scroll_area.setWidgetResizable(True)
       self.scrollAreaWidgetContents = QWidget()
       self.scrollAreaWidgetContents.setGeometry(QRect(0, 0, 500, 300))
       self.grid_layout = QGridLayout()
       self.grid_layout.addWidget(self.a_widget_ui(), 0, 0)
       ... # Set other widget to grid_layout in position of (1, 0), (2, 0), (3, 0)
        
       self.button_box = QDialogButtonBox(QDialogButtonBox.Ok | QDialogButtonBox.Cancel)
       self.button_box.accepted.connect(self.accept)
       self.button_box.rejected.connect(self.reject)
       
       #set the buttonbox at the end of gridlayout
       self.grid_layout.addWidget(self.button_box, 4, 0)
       self.setLayout(self.main_layout)
       self.setGeometry(300, 300, 790, 800)
    
    def self.a_widget_ui(self):
       group_box = QGroupBox('A Information')
       
       a_list = ['1', '2', '3']
       self.combo_box = QComboBox()
       self.combo_box.addItems(a_list)
       self.combo_box.activated[str].connect(self.update_widget)
       
       self.stacked_layout = QStackedLayout()
       self.A_layout = A_Layout()
       self.B_layout = B_Layout()
       
       self.stacked_layout.addWidget(self.A_Layout)
       self.stacked_layout.addWidget(self.B_Layout)
       
       hbox = QHBoxLayout()
       hbox.addWidget(self.combo_box)
       vbox = QVBoxLayout()
       vbox.addLayout(hbox)
       vbox.addLayout(self.stacked_layout)
       group_box.setLayout(vbox)
       return groupbox
    
    def update_widget(self, choice):
       if choice == "A":
          self.stacked_layout.setCurrentWidget(self.A_Layout)
       else:
          self.stacked_layout.setCurrentWidget(self.B_Layout)

Then I have these different layouts for A_Layout() and B_Layout()

class A_Layout(QWidget):
    def __init__(self, parent=None)
        super().__init__(parent)
        grid_layout = QGridLayout()
        grid_layout.addWidget(self.set_a_widget(), 0, 0)
        self.setLayout(grid_layout)
    
    def set_a_widget(self):
        main_widget = QWidget()
        self._a_attrib = QLineEdit()
        self._b_attrib = QLineEdit()

        form_layout = QFormedLayout()
        form_layout.addWidget('set a attrib', self._a_attrib)
        form_layout.addWidget('set b attrib', self._b_attrib)
        main_widget.setLayout(form_layout)
        return main_widget

class B_Layout(QWidget):
    def __init__(self, parent=None)
        super().__init__(parent)
        grid_layout = QGridLayout()
        grid_layout.addWidget(self.set_a_widget(), 0, 0)
        self.setLayout(grid_layout)
    
    def set_a_widget(self):
        main_widget = QWidget()
        self._a_attrib = QLineEdit()
        self._b_attrib = QLineEdit()
        self._c_attrib = QLineEdit()
        self._d_attrib = QLineEdit()

        form_layout = QFormedLayout()
        form_layout.addWidget('set a attrib', self._a_attrib)
        form_layout.addWidget('set b attrib', self._b_attrib)
        form_layout.addWidget('set c attrib', self._c_attrib)
        form_layout.addWidget('set d attrib', self._d_attrib)
        main_widget.setLayout(form_layout)
        return main_widget

There are some conditions that I've made when I was making this structure.

1. I made class A_Layout and class B_Layout in order for me to reuse those Dialog later if needed.
2. I used QStackedLayout / QStackedWidget in order for me to update the layout/widget via combobox.

My questions are the following.

1. Is it possible for me to change the layout size dynamically? For example, as you can tell that the size of layout will be different between A_Layout and B_Layout due to the number of components.
2. Since I am pretty new, but I have a hunch that I am doing it completely wrong about using qstackedwidget, maybe I should customize the layout such that it would work as qstackedlayout but has more size management

I would sincerely want to get advice or suggestions if it's possible. What I have tried is to put QSizePolicy before adding layout/widget in stackedlayout and put them whenever I call update_widget. Any other tip or advice would be very appreciated.