doubtful vs in question

doubtful and in question both are adjectives.

Word	Noun	Adjective	Verb	Adverb
doubtful	No	Yes	No	No
in question	No	Yes	No	No

As adjectives, doubtful and in question are synonyms defined as:

Other synonyms of doubtful include dubious, dubitable.

doubtful (adjective)	in question (adjective)
open to doubt or suspicion	open to doubt or suspicion
fraught with uncertainty or doubt
unsettled in mind or opinion