Would we need a business visa for this trip?

OceanBeach has given you a good advice.  However, based on your username, I'm thinking there's a good chance your parents were Vietnamese immigrants.  If that's the case, the best "visa" for you is VEC (Visa Exemption Certificate). 

VEC is THE non-visa-visa for Vietnamese-American, or American born whose parent/s is/are Vietnamese, or American who is married to Vietnamese, or American who is married to another American with Vietnamese roots -- you get the drift.  It gives you multiple entry for 5 years, with 180 days as the maximum length per stay.

VEC doesn't allow you to work but you can do everything else as long as you don't draw income from the activities.

In Santa Ana, there are dozens and dozens of travel agencies who can help you with the application.  They do charge a lot more than if you do it yourself ($80 for them to do the work vs $10 if you fill out the document and send to DC with a stamped certified envelope or trackable FedEx, UPS for returned documents.)

1- As the VEC is good for 5 years, make sure that your passport will not expire until 5 years and 6 months from the day of your application.  If it does, you MAY run into problem for your later trips.

2-  If your passport has plenty of years and pages left, make sure to request that the VEC is glued onto a page of your passport.