family is/are? (Singular or plural?)

The family _______ (is/are) cleaning the house.
Which answer is correct? Is or are?

In American English, family is always considered as a singular noun.
Therefore, the answer is 'The family is....'

HOWEVER;

For British English, 'family' can be a singular noun or a plural noun.
When you are referring 'family' as a single unit or think of them as a group, you use 'is'.
When you are referring 'family' to the individuals (family members), it's more common to use 'are'.

For example;
1) My family is big. It consists of 10 members. (singular)
2) My family are having lunch. They are having lunch at the restaurant. (plural)
*you cannot say 'It is having lunch at the restaurant' (singular)

Another example;
1) My family is big. (That means it consists of many family members.)
2) My family are big. (That means the family members are all fat/big.)

BACK TO THE QUESTION ABOVE, WHICH ANSWER IS CORRECT? IS OR ARE?

I knew or I've known (him for years)?

I knew him for years. - This is correct but is used if the person mentioned has died.
I've known him for years. - This is more accurate. It shows that the person is still alive and you still know him until now.

However, can we use "I've been knowing him for years" (Present Perfect Continous Tense)?

Present Perfect Continuous Tense is used to show that something started in the past and has continued up till now.

Therefore, formally, it's correct to say;
- "I've been living here for years"
but not, "I've been knowing him for years."

WHY???
It's because there are some verbs that we do not usually use in progressive (continuous) forms. They are mostly verbs of sensations and mental states.
For example;
 like, love, need, prefer, know, seem, mean, own, hate, want,
wish, desire, see, hear, feel, notice, understand, remember, forget, believe, recognize, appear, possess, contain, consist, etc.

Of course you don't say, "I'm liking the food" when you can just say "I like the food" or "I'm loving/believing/knowing you" if you can just say "I love/believe/know you".

ANYWAY, AS THE VERNACULAR (SPOKEN LANGUAGE), THOSE EXPRESSIONS ARE SOMETIMES USED AND ARE ACCEPTABLE. 

playing football 'ON the field', 'AT the field' or 'IN the field?

Based on my references, it's actually 'on the field'. (British English)

E.g.: The children are playing football on the field. (for a playing field)
BUT; The cows are grazing in the field. (for a field with crops)


*The preposition 'in' is also used for 'playground', 'park' and 'garden'.
*The preposition 'on' is also used for 'beach' and 'farm'.
*The preposition 'at' is also used for 'market', 'school', 'hospital' and 'airport'.

However, when you refer to a meeting point, you can use 'at', for example; "Meet me at the school field."