Hello Megan from Indiana!
So you do have to pay admission to get into
Disney Quest. There is no viewing-only admission for Disney Quest.
You used to be able to see tickets prices to Disney Quest on the website, but in the update that seems to have gone away. But no worries, you can just get a ticket at the entrance.
But what is the cost?
Of course it can change over time, but when I was there earlier this fall a one-day pass cost just under $50 for an adult, and just a bit over $40 for a child (ages 3-9). Those prices include tax. As with most other things at Disney, ages under 3 are free.
So dependent upon the rules tied to your free tickets, I would use the two tickets for the two adults, and pay for the child. That should save you almost $10.
Write me back if this fellow Hoosier can help with any other questions!
Have a magical vacation!