The use of 几 and 都
几 (jǐ) is an interrogative adjective used to ask how many? It is used when asking about small numbers, usually less then 10.
Example:
几口人? Jǐ kǒu rén? How many people?
都 dōu is an adverb meaning 'all'. It appears before the verb but refers to the preceding
subject.
Example:
他们都是老师. (tāmen dōu shì lǎoshī.) They are all teachers.