伙 huǒ - measure word

一伙 [yī huǒ], measure word, means a group of people.

一伙歹徒 [dǎi tú] a group of gangsters or thugs

一伙青年人 [qīnɡ nián rén] a group of young people

一伙游览者 [yóu lǎn zhě] a group of tourists

一帮 [yī bānɡ], 一拨 [yī bō], 一伙 [yī huǒ], 一批 [yī pī], and 一群 [yī qún] can be used interchangeably when referring to a group of people, though 一群 [yī qún] is more formal than the others.

一帮 [yī bānɡ] and 一伙 [yī huǒ] usually impart a derogatory connotation, for example,

一帮强盗 [yī bānɡ qiánɡ dào, a gang of robbers]; 

一伙歹徒 [yī huǒ dǎi tú, a gang of scoundrels].

一拨 [yī bō] and 一批 [yī pī] are used when referring to a group of people who are taking part in an activity or are on the move, for example,

公司又来了一拨/一批新雇员。 [Gōnɡsī yòu lái le yī bō/yī pī xīn ɡù yuán. Another group of new recruits has come to the company.] 

Of these, only 一拨 [yī bō], 一批 [yī pī] and 一群[yī qún] can be used to refer to non-human objects. 一拨 [yī bō] and 一群 [yī qún] are used to refer to animals and other non-humans, live organisms, whereas only /一批 [yī pī] is used for non-living things. For example

河里又来了一群鱼/一拨鱼。[Hé lǐ yòu lái le yī qún yú/yī bō yú. There comes another school of fish.]

图书馆来了一批新书。[Túshūɡuǎn lái le yīpī xīn shū. The library has acquired a batch of new books.]