Use mode='markers+lines' and additional attribute marker=dict(size=sizes1)
In my case I mark only value contain (2,6,9)

sizes1 = [10 if y in (2,6,9) else 0 for y in seed1_y_data]

trace1=go.Scatter(x=x_data,y=seed1_y_data,mode='markers+lines',name='Team A'
                  ,marker=dict(size=sizes1))

data=[trace1]
layout=go.Layout(title='This is line chart',
                 xaxis={'title':'this x axis'},
                 yaxis={'title':'this y axis'},
                 )
fig=go.Figure(data=data,layout=layout)

pyo.plot(fig,filename='line.html')