1. Slice: Thinly slice the fresh lemons and chop the whole oranges, keeping the peels entirely intact on both fruits to maximize the natural pectin content.

2. Measure: Your knife work should yield approximately 1 cup of thin lemon slices and 3 cups of chopped orange pieces.

3. Soak: Combine the prepared sliced lemons, chopped oranges, and 4 cups of water together in a large mixing bowl.

4. Soften: Let the citrus bowl rest undisturbed for 12 to 18 hours in a cool place, allowing the liquid to extract flavor and soften the rinds.

5. Boil: Transfer the entire soaked citrus mixture and its liquid into a large pot and cook over medium-high heat for 30 minutes until the peels are tender.

6. Cool: Remove the large pot from the stove and let the hot citrus mixture cool down completely to room temperature.

7. Stir: Mix the peeled, chopped, and seeded prickly pears along with all 6 cups of granulated sugar directly into the cooled pot.

8. Thicken: Return the pot to medium heat and cook, stirring frequently to prevent burning, for 25 to 30 minutes until the jelly begins to sheet or coats the back of a spoon.

9. Sterilize: Submerge your glass canning jars in a boiling water bath while the fruit simmers to sanitize them thoroughly.

10. Fill: Ladle the bubbling hot marmalade carefully into the hot, sterilized half-pint jars, ensuring you leave exactly 1/4 inch of empty headspace at the top.

11. Seal: Wipe the jar rims clean with a damp cloth, center the flat lids on top, and screw the outer bands down until they are just finger-tight.

12. Process: Lower the filled jars carefully back into the boiling water bath and boil rapidly for 5 minutes to fully exhaust air and seal.

13. Rest: Lift the processed jars out of the water bath and set them on a towel-lined counter to cool completely without moving them.

14. Test: Press down on the center of each cool lid after 24 hours to check the seals, ensuring the metal does not click or pop back up.

15. Label: Write the recipe name and current date on the outside of your sealed jars before storing them away in your pantry.

16. Savor: Pop open a perfectly sealed jar of this exotic preserve and celebrate your mastery of home canning!