adding lines to current AT&T plan?

[Lady V]

Hello! We currently have 2 iphones and 1 tablet on our plan with AT&T. I am interested in adding 2 more phones (nothing fancy/talk and text) to our plan. Does anyone know of any discounts or promos coming out to make this as cheap as possible? We currently pay $160 for our plan and never use it all or even come close. We are hoping to add 2 phones and not have much of an increase in our bills. Maybe if we brought our own phones? Any advice would be welcomed!! Thank you!