So how am I supposed to unlock Rod and Todd?

Reason why I ask if you completed level 31 was I had a task left with Wolfcastle. And it let me level to 32, but it did not let me prompt Lisa until Wolfcastle completed his final task

Yeah, I completed level 31 twice (getting bonus donuts). When I logged in today, all I got was a quest about making Bart spend time with Grandpa but Lisa didn't say anything.

Edit: having read your second post, I am currently building Wolfcastle's house.

It should unlock once you finish Wolfcastles tasks

According to the wiki, it should trigger from Lisa if Sir Putt-a-Lots is already built, just like you said. I guess I'll just wait and be patient. Or perhaps it'll trigger after I finish building Wolfcastle's mansion and doing his tasks.

http://simpsonswiki.net/wiki/The_Simpsons:_Tapped_Out_Level_32_update

Yeah, you've got a few tasks to complete before they arrive. Be patient, finish tasks, and you will be rewarded, grasshopper!