Cops working motors are taught and trained how to park their motors.
How many are allowed to take breaks/meals together depends on the practices & policies of any particular agency, and can be affected by the nature of their detail/duties at that time. (It's not uncommon for agencies to have limitations on how many officers routinely can be seen together for coffee breaks & meals, as this is the sort of thing that can result in unwanted PR issues, public perception issues, etc.)
As far as how they were sitting? Yep, if they were seated facing each other, they ought to have been able to cover all directions. That freedom of vision ought to have been able to be applied to outside the windows to some extent, too. Doesn't mean it would have been obvious, though. Sometimes the appearance of deliberate attention serves a purpose, and sometimes discrete attention to surroundings is more useful. Watching without appearing to be watching is handy in a public situation, and it helps ease potential friction (since some folks can get nervous if they think cops are watching them).
Now, cops are people, too. I've certainly known enough guys & gals who didn't always have their officer safety awareness up and engaged in all situations and circumstances.
The four officers shot & killed in Lakewood WA (Nov '09) was a tragic reminder of how someone looking to kill police in public can take advantage of when officers may be taking a break or a meal in public.
Whenever I used to stop for coffee or a meal with a partner (whether working uniform or plainclothes), most of the other cops with whom I met were always aware (without being obvious) of all directions, the general presence and movement of the public and any changes in the crowds of any size. (Sometimes a subtle crowd reaction, or undercurrent, can provide an early warning before a potential threat is itself visible.)
Retired LE - firearms instructor & armorer