If the others uploaded their tracks, then you should be able to see their boats on the water. If not go to the left slide out panel and open the “fleet” icon. Make sure all of the boats of interest are checked.
to see tracks you have to go to the “boat vs” tab (in the same left hand panel) and then select the two boats of interest in the drop downs at the top. Use the controls at the bottom of that panel to select length of track and other analytics.

I don’t know 2)