Thank for all the tips, I finally got me, on a 16 people server.  It is not easy but still much easy than the titan drop pin.  I used to think the more people play, the better to get the pin. end up not easy to keep all flag under control long enough.

It really depend on your term.  I should have 2 but once I decide to stay behind to protect one of the flag.
Teamwork is the key.

THank for all who nice enough to share tips