Re: fortunately 3 do reasonable all you can eat data packages
The Mrs uses almost no data and they moved her to an unlimited plan at the same price as she'd been paying before and that is a lot cheaper than my son's one.
So when the Son's Plan comes up for renewal, I assume you will renegotiate to match your Mrs's Plan.
Alternatively, keep your eye's open for a better deal and migrate your son across to it, when his renewal falls due. If you're being savvy, you will do this via Topcashback and so get a generous 'new contract' cashback...