1. They ( to play ) football for an hours last

 They had been playing football for hours last Monday. В прошлый пн они играли в футбол в течение нескольких часов.

The sentence is in Past Perfect Continuous. Past Perfect Continuous is formed with the help of the auxiliary verb to have in past (had).  The auxiliary verb to be is used in the third form and we add -ing to verb. had + been + verb + ing.

Negative is formed with the help of not which stands after had. 

They had not been playing football for hours last Monday.

Interrogative is formed had + subject + been + verb + ing.

Had they been playing football for hours last Monday?