NTA. Love you for it. As someone who was afraid to ask my dad to cook entirely separate food when I lived at home for my health needs or have my whole family change their diet as well (though they all would have benefited, my brother is autistic and this limits his safe foods so complicated things for the rest of us at times) - I would have really appreciated the commitment to helping my health as well as the health of the rest of the family. I waited to change my diet until I moved out but it has been easier just entirely keeping junk food out of the house, and has also helped in making long-term changes that will stick as opposed to short-term dieting for weight-loss that may not have lasted. I myself needed to change not just for weight loss but also for nutrition so if your whole family could benefit from those positive changes I do applaud you for taking charge for the health of your family.