[ThePillenwerfer]

A bit more information would help.

You say the old 'phones won't ring but does that mean that the bells don't make a noise and that they otherwise work? In other words can they call each other but you simply don't know about it?

How are the telephones wired: the old way — using two wires and their internal capacitors or the modern way with three wires.

Do you get a dial tone? Does it go when you dial?

If it is just the bells it's certainly do-able as the Panasonic 206 works with either pulse or tone dialling. Hopefully somebody who knows about their intricacies will be along later with advise on how to set it up.