With a vegetable peeler, peel the skin of the fruits making sure there’s no pith attached to it. Thinly slice the peels and cut into small pieces or half. Transfer to a bowl and set aside.
Slice fruits to about ¼-inch thick. Take each slice and remove the pith as well including the center (if it’s white, it has to go). Place small pieces of fruit in another bowl separated from the peels along with any juices.
In a small bowl, whisk together ¼ cup sugar with pectin. Add to fruit pieces, stir well and set aside.
In a large pot, add peels and pour in 1 cup orange juice. Add baking soda and stir well. Bring the mixture to a boil, cover, reduce heat to low and simmer for 20 minutes.
When time is up, add fruit mixture including the juices and pour in the remaining orange juice. Stir once again and bring the ingredients to a simmer on medium heat. As soon as it starts simmering, start the timer for 10 minutes.
Stir in the remaining sugar into the fruit mixture and bring the ingredients to a full boil; cook for 2 minutes.
Remove from the heat and transfer the marmalade into prepared jars. Process the jars in a water bath for 15 minutes after the water return to a full boil.
Transfer jars on a rack placed in a draft-free area and let them cool off.
Note: The marmalade might take up to 48 hours before it sets up.