On the farm thingy, whatever the name is, bottom left. You'll see a key there, but it's locked behind a snake, you'll first need to progress through the other storyline.
Some of this you're asking is honestly just through progressing the story. Dull Blade is inside Heather's (is that her name ? The black haired milf) house. You can still get inside Ella's house post-scene, and you can get inside her room post-scene as well, bottom right of the house. Broken handle is also in Heather's house, you need to do their little quest of getting the caterpillars and fertilizer. It's in the garden, right side.
Edit: Adding screenshots for these things. Chest key for Maximus, and the rest is for Jklife.