Hello Complexity. You are correct that the confirmation notice for purchasing the Brokerage Account says that the increase was 1%. It is a text glitch that we hope to have fixed in our next update, which we are currently testing.
You can assure yourself that your family did indeed get a 2% boost by tapping the Bank button and review the Current Daily Interest Rate: % information. If you purchased 1 Brokerage Account, the interest rate should say 3%.

If it doesn't, please let us know.