Hi
Welcome to Infopath Forums!!
Follow below steps:
1.Open infopath in design mode
2.Right click on the text box
3.Select Text Box Properties
Result:Text Box Properties window will open
4.Click on Data Validation button
5.Click on Add button
6.Select the Radio button control name in the first dropdown
7.then Select 'Type a nUmber' in the third drop down
8.Enter '1' number
9.Second dropdown value will 'is equal to'
10.Enter the text in either ScreenTip or Message text box
11.Click Ok
12.Click ok
13.Click ok
14.Repeat the same steps for Second text box control.
15.Save the form and preview it.
Result:When the radio button is selected first and second text boxes will become required fields