"A new family are coming to the neighbourhood" was marked as incorrect, but in UK English the use of plural is normal. See https://blog.harwardcommunications.com/2017/02/07/the-family-is-or-the-family-are/
This blog mostly discusses cases in which the definite article precedes the noun, and when the definite article precedes the noun, there are times when either “is” or “are” are acceptable.
However, in the sentence we’re working on here, the indefinite article precedes the noun, and the indefinite article usually goes with a singular subject. Therefore, “a family is” is correct, rather than “a family are”.