In batting: 30 points for 100+ runs, 20 points for 75-99 and 10 points for 50-74. It's maximum is 30 points, so a double century still only gives 30.
In bowling: 30 points for 5+ wickets, 20 for 4 and 10 for 3. Maximum of 30 again.
Your captain doesn't get those bonus points, just his overall score is doubled.