Rinse the jalapeños and remove the stems and seeds. Leave some seeds in if you want the jelly spicier. Finely chop the jalapeños, red bell pepper, and green bell pepper in a food processor or blender. You should have about 3 cups chopped peppers.
Add the chopped peppers, vinegar, salt, and sugar to a large heavy pot. Bring to a full rolling boil over medium-high heat. Boil for 5 minutes, stirring often.
Start by adding only 3 ounces of the liquid pectin. Stir well and boil for 1 minute. Skim off any foam that forms on top. Do a consistency test by spooning a little hot jelly onto a cold plate. Let it sit for 1 to 2 minutes, then tilt the plate. If it slowly thickens and moves like thick syrup, it is ready. If it is too runny, add more pectin 1 ounce at a time, boil for 1 minute, and test again.
Ladle the hot jelly into clean half-pint canning jars, leaving 1/4 inch headspace. I like to use a canning funnel to prevent spills. Wipe the rims with a damp paper towel. It should fill about 6-8 half pint jars or 3-4 pints. Add lids and screw bands on until fingertip tight.
Process jars in a boiling water bath for 10 minutes, adjusting for altitude if needed. Remove jars using a canning jar lifter and let them cool undisturbed for 12 to 24 hours.
Once the jars have cooled, remove the bands, check the seals, label the jars with the date to track freshness, and store in a cool, dark, dry place. Let the jelly set for at least 24 hours before serving.
Serve over cream cheese with crackers, or use as a glaze, dip, or spread.