From a diabetes perspective, small meals, eaten often seems counter-intuitive. The biggest reason is that it offers less time between meals for BS to return to normal.. Of course, the other perspective is that avoiding larger meals means potentially avoiding larger spikes. Also, eating larger meals can often leave people 'wiped-out', and less possessed of the energy to engage in exercise, for instance.
In this case (and bear in mind I'm not qualified to say), especially given your age, I'd be inclined to agree with your mother i.e that perhaps you should just concentrate on weight-loss.
That doesn't mean you can get away with really bad food choices. Rather, losing weight should not only bring with it a commensurate lowering of BS, but will also likely make you feel more inclined to bouts of exercise, which should compound the effect. More than that, it might make it easier to eat better at home, especially as your mum probably finds it easier to get her head around someone on a diet having special requirements when it comes to meal-times.
Lastly: Is there anything to stop you from preparing your own separate food, alongside what you're preparing for your family? That way, they feel no pressure to change what they want to do, and you still get to enjoy the company of the family dinner.
