Sorry, I misunderstood your use case.
In that case, you could just pass the window handle to your scripts (which is basically a string) and use it to plot to the same window:
viz = Visdom()

# line updates
win = viz.line(
    X=np.column_stack((np.arange(0, 10), np.arange(0, 10))),
    Y=np.column_stack((np.linspace(5, 10, 10),
                       np.linspace(5, 10, 10) + 5)),
)

# Save or pass win to the other scripts and use it to append to this window

# In other scripts:
win = 'window_371666b9beb910'
viz.line(
    X=np.column_stack((np.arange(20, 30), np.arange(20, 30))),
    Y=np.column_stack((np.linspace(5, 10, 10),
                       np.linspace(5, 10, 10) + 5)),
    win=win,
    update='append'
)