J.,
Regardless of what you believe for sugar, salt, breastfeeding, formula, whatever, you have to be there for your kids.
Anyone who doesnot regard your wishes/desires/needs for your children as tantamount to their own is not working in your children's best interest. Family included.
I hope you receive this and understand that I have read quite a bit from others who have actually had to cut off family visits/connections for a while for them to get the message that running roughshod over what they the parents wanted was not only not okay, but not to be tolerated.
This may sound extreme, but it is what one Mom I met HAD to do. Her son has multiple sensitivities for food, as well as behavioral issues related to food, and other issues as well. Grandma, thinking the Mom is making all this up and sneaking her son a delicious cookie was not only NOT helping, but very damaging. 6 months to undo a simple cookie! Aunties thought the same thing. After going to NYC and other locations to get her son diagnosed with his sensitivities and other problems (it took awhile to get a pediatrician who understood that his activities were just NOT normal), everything is just trampled on by a simple cookie. I am still in awe of her for doing this. It doesn't just take guts. It takes stamina and fortitude and a whole host of courage.
You are nowhere near overbearing. You are not overprotective. You are being a MOM and you are being way too soft on them, IMO. Location, food intake, anything.
I'm sure this sounds rather over-the-top, but then you haven't GOT food sensitivities for your children. What happens if you do? What sets the stage for them to listen to you - believe you - and follow YOUR directions with YOUR children because YOU are responsible?
Good luck hon, you are going to need it. I hope you keep in touch and if you need an ear, I'm here.
M.