You would need 8 of those to upgrade 4 roundtrip tickets (each good for one way). The Fall/Winter isn't as tough as the summer, but 4 people is a stretch if you don't have any status with the airline.
You would call ahead, tell them what coupon you have and ask to get on the meal list - sometimes they cater enough food for paid/confirmed seats only and will leave seats empty if they don't have enough meals, even though there are people who wanted to upgrade.
Getting on the meal list in no way puts you on any other kind of upgrade list - you still have to check in for your coach seats and politely ask the agent to put you and your 3 companions on the upgrade list. Ask him/her how many people are ahead of you vs. how many seats are available and you'll have an idea. Will you take all or none, or will you accept 2 and send your wife and one kid to the back? Decisions...decisions...