When meaning 'a group/party,' 行 is read xíng (second tone). Don't confuse with 一行 (yī háng) meaning 'one row/line' - different pronunciation, different meaning.
usage
一行 is formal and often used in news or official contexts. The pattern is: person/group + 一行 + number of people (optional). For example, 校长一行三人 (the principal and a party of three).
