Good luck on your in laws, I would just chock it up to letting grandma spoil them.
Yes, i do have advice on kicking a sugar habit. First of all cold turkey IS NOT a good idea like it is with most things. Your blood sugar is a tricky balance and eliminating it completely will/can send you into a diabetic-like shock. Sugar is not all you have to worry about though, white bread and white pasta (anything with white flour) is like eating white sugar. Its basically empty carbs that trick your body into thinking its actually getting fed and it revs up your insulin only to find the fiber to process it.........lacking. Ive done a bit of research on this because diabetes was a factor in the death of my father and my grandmother. It runs in my family and i swear its not going to get me, my husband or my kids.
Stave off of sugar little by little, replace your syrups with lower spiking sugars like agave nectar or grade b maple syrup. Pick up some stevia, its a powder or liquid that is extremely sweet, you only need a little and it can sweeten your beverages (coffee, tea, smoothies, etc.) like a pro. I used to drink the heck out of diet soda but now i just buy sparkling water and put a little stevia in it, maybe lemon too, and i dont miss it.
Never cook with white flour and white sugar, stay away from white pasta. the bread, flour and pasta that has brown flecks in it are your friends. you can also Add a little flax seed meal to your baking to amp up the fiber. Raw sugar or date sugar are good subs for white sugar also.
Lastly have your blood sugar tested , if it is too high there are a few things you can buy to regulate this. Chromium picolinate, bitter melon extract and cinnamon extract are very effective at quickly regulating sugar levels. But you still need sugar, fresh fruit and complex carbs will give you the kind of sugar that your body will thrive on.