Look into Consumer Cellular. You can get JUST talk and text. You pretty much can build the plan you want. All members share data, but ONE person in charge can determine when to shut it off for any other. No contract – first month is free. We love them!
I don’t know where you live or how much you need to use your 3rd line, but there are companies that have a low rate for just text/talk. There’s also very cheap rated companies too for prepaid cellphones