No, you can' t. Only if it is for example al pranzo di famiglia (at the family lunch)
The sentence says, "They are at lunch," not "They are at the lunch." Knowing this information, let's look at this: a=at (or to) il=the (if it was a feminine word like "cinema" then it would be "la", not "il")
now we combine the two words to create "al", so: a+il=al now we can assume: a=at il=the al=at the
So if you understand that, then you'll understand this: They are AT lunch=loro sono A pranzo (a=to)
So the word "al" would be if the sentence was: They are AT THE lunch=loro sono AL pranzo
I hope this wasn't confusing. Good luck :D
No they shouldn't. The verb for "have" is "avere" and "to be" is "essere". So it would be Loro hanno pranzo...which is pretty much an entirely different sentence.
Ooh, so how is a listener going to distinguish between "a" - at and "ha" - he/she/it has?
Context? If you have the verb form "are" before (sono), how could "a" be "ha"?