art
Ark
ail
Nap
cog
Successfully is a 12 letter word with three set of double letters. Stubbornness is another 12 letter word.
Wit
Got
mor
Kid.
Pal, bro, cuz, sis
Depending on the context, "hut" or "rid."
If it's three letters, it's "hug". If it's four letters, it's "kiss".