oh love, i know the feeling.
sometimes it seems impossible to lose the weight when other people in your family are not quite as motivated.
the way i have started is by offering to help and cook the food for your family, rather than putting the burden on them to make the changes. you will earn brownie points for cooking dinner every night and taking away from her stress load, but you can also control what goes onto your plate at the same time!
hope this helps!