So the Succubus village is only opened once you trigger an event. You need to head to the abandoned house in the slums and eat the food in the basement. Once you eat 15 (so 3 each day over 5 days) you'll be attacked by a succubus. (Note: If your below size 5, you will lose automatically and it will lock the event from happening ever again). After you beat her, she will run. Go to Esmerelda's house and she'll let you use the portal.
Finish the Quests in the village and the two sisters will be there.
The slimes once they hit "adult" stage, need Supercharged Slime to grow any bigger. You can get it from Aria (Joe's secret pet). To unlock her, help Joe with his slime culling 5 times and he'll show you. Otherwise just eat him and play with the control panel.
You get the slime from aria by giving her captured Jello Slimes.
Hope this helps!