Bart or marge?

For Bart, you have to be Level 12 and purchase Bart's Treehouse. It's a nice instant-build. If you are getting tasks for earlier buildings and are Level 12+, you are ahead of the game, no bug.

For Marge, you need Level 15 and you have to purchase Moe's Tavern.

I realize I need Bart's treehouse but that says it's Bart Crusoe Pt. 2. The Simpsons wiki quest guide indicates Bart Crusoe Pt. 1 is to send Lisa and Milhouse to school. Do I have to be prompted to do that or can I just select that out of their respective available quests?

You always have to be prompted for a quest. And everything is in order. So just wait and try to be patient. I know it can get frustrating, but it will come.