Hi Sean,
How were you inputting your design requirements? For these once you're in WEBENCH hit the NEW buon and input you Vinmin,Max Vout1 Iout1 and then your second set into Vout2 and Iout2 this should then show the LM5119 Dual design.
For a shortcut please try this link though:
http://webench.ti.com/webench5/power/webench5.cgi?base_pn=LM5119&VinMin=30&VinMax=55&O1V=24&O1I=5.4&O2V=12&O2I=5
If this still doesn't work let me know and I can share a design with you at your email address.
Best regards,
Tommy