Gheist

Oh sure, I didn't know whether you had gotten it already or not.

To trigger the scene, you just need to walk into the cave to the left of Taelia's house right BEFORE you walk in to the house to find out that she was kidnapped. Then just exit the cave via the northern exit and the scene should trigger.

She gets kidnapped right after you find the meteor after Cella chases you off so after that just do not go into the house and go to the cave instead.

After the scene triggers you just need all 18 Pokemon and you will get the true ending. Everything else except the one scene where you rescue Taelia from the bandits is exactly the same so you can skip past the text if you want.

Hope this helps. Oh and the Banette was around their base like you said so thanks for that.