[illi s7aab ktir]
Why is it not ktirin?

 

It's the plural of kteer = many.

 

He's asking why it's not إلي صحاب كتيرين

 

In Palestinian Arabic:

كتيرين is almost never used; you can safely eliminate it from your active vocabulary.

إلي صحاب كتير = إلي صحاب كتار

You can use either.

 

Can I use كتار interchangeably with singular and plural nouns?

 

No. ktaar is only plural.

 

Thank you all