Successfully is a 12 letter word with three set of double letters. Stubbornness is another 12 letter word.
'What' is a four letter word, 'for' a three letter word, 'which' has five letters, 'yet' is spelled with three while 'it' has only two.
bladders
balloon
Mississippi
baldnessbaseballbaselessbluenessboldnesscalmnesscarelesscarefreecluelesscoldnessdistressduckbilldumbnessdampnessdeafnessevennessfairnessfondnessfortressgladnessgoddesshardnesshairlesshomelesskindnesslistlesslifelesslovelesslatenessmattressmeannessmindlessneedlessoverpassopennesspainlessplaybillprogressrainfallrecklessrudenessruthlesssamenessseedlessselflesssicknesssnowballsnowfalltimelessuglinessvastnesswindfall
'What' is a four letter word, 'for' a three letter word, 'which' has five letters, 'yet' is spelled with three while 'it' has only two.
bookkeeper
The following words have three consecutive sets of double letters:bookkeeperbookkeepersbookkeeping
bladders
the word 'letter'?
balloon
coffeetoffeebarroomtattoocoffeepotraccoonlesseeputteecoollysettee
Mississippi
baldnessbaseballbaselessbluenessboldnesscalmnesscarelesscarefreecluelesscoldnessdistressduckbilldumbnessdampnessdeafnessevennessfairnessfondnessfortressgladnessgoddesshardnesshairlesshomelesskindnesslistlesslifelesslovelesslatenessmattressmeannessmindlessneedlessoverpassopennesspainlessplaybillprogressrainfallrecklessrudenessruthlesssamenessseedlessselflesssicknesssnowballsnowfalltimelessuglinessvastnesswindfall
A three letter word for bother is bug
flee
cOOEE