One day ahead...
Prepping the kumquats:
Slice the fruits in half and separate the flesh from the skin. Thinly slice the rind. You'll have about 2 cups of kumquat rind.
Gather all the pulp into a blender and pulse 2-3 times until coarsely chopped. Strain the juice through a fine-mesh sieve. Set aside 1/3 cup of kumquat juice and reserve the rest for making kumquat drink.
Prepping the tangerines:
Zest the tangerines with a fine mesh microplane, being careful to take only the thin orange skin, not the white pith beneath.
Peel the tangerines and divide them in half. Remove the membrane wall on one side around a segment. Apply a little pressure on the segment with your thumb to separate the segment along the next membrane (you could also use a paring knife but don't cut the fruit; use the knife as a separator). Loosen and free the segment and gently pull it away from the fruit, removing all the membrane. Repeat and remove the rest of the segments. This technique releases and spills less juice. Transfer the tangerine segments with as much as juice as possible into a bowl. I gathered 2-½ cups of tangerine pulp. Set aside.
Making tangerine-kumquat marmalade:
In a pot, combine the sliced kumquat rind, kumquat juice, tangerine zest, tangerine pulp, sugar and 1-½ quarts of water. Bring to a boil, then lower the heat to a medium-low and cook for 15 minutes. Remove from the heat. The content should be syrupy. Cover, set aside and let sit overnight (at least 18 hours) at room temperature.
The following day, bring the citrus mixture to a boil, then reduce to a simmer for about 40 minutes. Stir every now and then using a wooden spoon. Bring back a boil. Skim any foam that develops on the top before pouring into the Mason jars.
Using a paring knife, scrape and gather all the grains of the vanilla bean. Add the vanilla beans and vanilla extract to the marmalade.
Fill a large pot of water and bring to just under a boil. Place the Mason jars, lid, heat-proof funnel and tongs in the pot and let it boil for 10 minutes. Be sure to read the instructions that come with your Mason jars. They'll give you exact time and techniques.
Remove the jars from the water and fill with tangerine kumquat marmalade, leaving about ¼-inch of head space or whatever your canning directions say. Carefully place the lid on the jar. Tighten the collar around each jar. Bring your large pot of water to a boil and place all the sealed jars in it for 10 minutes.
Remove the jars from the water. If the top of the lid still pops, the vacuum didn't form and you'll need to consume the jam in the next couple of weeks, storing it in the refrigerator. Otherwise you can safely store it in your pantry for up to a year.
To insure good sterilization of the product, I stack a dozen magnets together to create a stick and use it as a gripper to place the lids on the jars without touching them. Just make sure the magnets are clean!
After scraping the grains of vanilla, do NOT discard the remaining vanilla bean. Just place the vanilla bean in a jar and cover it with regular granulated sugar. Let it sit for a few weeks and you'll have fragrant vanilla sugar (great with plain yogurt).
If you don't have any vanilla bean, you can double the amount of vanilla extract.
The next day, when you bring the marmalade back to a rolling boil for the second time after simmering for 40 minutes, your candy thermometer should read 220°F.
Another test to see if the jam is done is to place a drop of it on a cold plate. After it cools down (2 minutes), if you tilt the plate and it stays in place, it's time to put it into the jars.
The marmalade will taste better if you let the sealed jar sit for at least a week before opening.