If you do choose to get the Hawaiian Airlines credit card (with its normal 35,000 miles bonus), please note that you can get a better offer by making a mock booking on the HA website.

When you get to the payment screen, select that you will be paying with a credit card (you don't need to complete the mock booking) and a 50,000-mile offer will pop up.

Edited to add: You and your wife could each get the card, and your child could use the "50% Off companion discount".

Note: Often, but depending on the season and actual dates, you can get a roundtrip in coach for just 50,000 miles. And even if the number of miles required is a bit higher, you can pay with miles + cash.