You're getting RR credits and ticketless travel funds mixed up. In the upper right hand corner of the SWA website there is a drop down menu for Travel Tools. Click on the arrow and select Travel Fund Balance from the menu (it's in the 3rd section of the menu). Enter your confirmation number from the previous flight and it will show you the amount of funds you have on account. If all 3 tickets were on the same confirmation number it will show you 3 names and $8 in travel funds for each person. To use the funds you just book your tickets as usual and when you get to the payment method part choose the option to use travel funds, enter the confirmation number and it will apply the funds to your new reservation. The funds have to be used by the person whose name was on the original ticket, i.e., you can't use all $24 for yourself, if you are the only person traveling.
When you select "Where are my old credits?" it is showing you the RR credits from your previous flights that occurred before they changed RR over to the current system. So yes you do have credits for the tickets you booked a year ago. But you won't have credits for tickets that you booked for anyone except yourself. The credits go to the individual whose name is on the ticket, not the person who paid for them.