How to make that there aren't identical values ​next to each other while randomizing and disable entry in text field?

So I have this Python code that generates pseudorandom numbers with tkinter GUI:

def ButClick():
    try:
        MinNum = int (txt1.get())
        MaxNum = int (txt2.get())
        Num = int (txt3.get())
    except ValueError:
        messagebox.showerror("ValueError", "Check if you typed in correct! You can't type in text! Numbers only!")
    else:
        Nums = ''
        if MinNum <= MaxNum:
            i = 0
            while i < Num:
                numOne = randint(MinNum,MaxNum)
                Nums = Nums + " " + str(numOne)
                i += 1
            scr.insert(INSERT, str(Nums) + "\n")
        else:
            messagebox.showerror("NumError!", "Your Min Number can't be higher than your Max Number or vice versa!") 
    pass

def remove_text():
    scr.delete(1.0,END)

def confirm():
    answer = askyesno(title='Exit',
                    message='Tired of randomness?') 
    if answer:
        root.destroy() 

root = Tk()
root.title("Hey")
message = Label(root, text= "Welcome to random numbers generator! Developed by Yaroslav Poremsky")
message.pack()

root = Tk()
root.title("Random is so random :)")

lb1 = Label(root, bg = "green", text = "Min number") 
lb1.grid(
    row = 0, 
    column = 0, 
    pady = 10, 
    padx = 10) 

txt1 = Entry(root, width = 30) 
txt1.grid(
    row = 0,
    column = 1,
    pady = 10,
    padx = 10)

lb2 = Label(root, bg = "orange", text = "Max number")
lb2.grid(
    row = 1,
    column = 0,
    pady = 10,
    padx = 10)

txt2 = Entry(root, width = 30)
txt2.grid(
    row = 1,
    column = 1,
    pady = 10,
    padx = 10)

lb3 = Label(root,  bg = "pink", text = "Number")
lb3.grid(
    row = 2,
    column = 0,
    pady = 10,
    padx = 10)

txt3 = Entry(root, width = 30)
txt3.grid(
    row = 2,
    column = 1,
    pady = 10,
    padx = 10)

but = Button(root, width = 15, height = 2,  bg = "magenta", text = "Generate", command = ButClick) 
but.grid(
    row = 3,
    column = 0,
    columnspan = 2, 
    pady = 10,
    padx = 10)

but_remove = Button(root, width = 15, height = 2, bg = "crimson", text = "Remove", command = remove_text) 
but_remove.grid(
    row = 3,
    column = 1,
    columnspan = 2,
    pady = 15,
    padx = 20)

but_quit = Button(root, width = 15, height = 2, bg = "violet", text = "Quit", command = confirm) 
but_quit.grid(
    row = 3,
    column = 3,
    columnspan = 2,
    pady = 15,
    padx = 20)
scr = scrolledtext.ScrolledText(root, bg = "grey", height = 10) 
scr.grid(
    row = 4,
    column = 0,
    columnspan = 2,
    pady = 10,
    padx = 10)

root.mainloop()

1. The problem is, when I enter the Min number of 0, Max number of 1 and Number of 12, sometimes identical values stand next to each other(Picture 1) Picture 1 How can I make that there aren't identical values ​​next to each other while randomizing?
2. The second thing is, I can type in this box(Picture 2) Picture 2 How can I disable entry in this field?

I've seen that it is possible to disable entry via creating a button, but can I make it without creating it somehow?