bookkeeping
accessoryaddressaggressiveannuallyappallassessassassinbitternessbuccaneerblurrinessbulletproofbutterballbuttresscassettecarelessnesscarryallcoffeecommissarycommissioncrabbinessfurrinesshappinesspennilesspuffinessruddinesssluggishnessstiffnessstillnessstubbornnessstuffinesssuccesstallnessvolleyballwellnesswheelbarrow
buccanneer
Those are consecutive letters in the English alphabet, starting with the letter 'k' and ending with the letter 'n'.
therein
therein
bookkeeper, bookkeeping
Successfully is a 12 letter word with three set of double letters. Stubbornness is another 12 letter word.
balloon
bladders
Savvy, letter, vacuum, and bubble have doubled letters.
addassallillofferrbeeseefeepeeteeweezooboocoogoomootoooddebb
No, "shuddered" does not contain a double consonant. It has two consecutive consonants "d" and "d," but they are not the same letter.