That sounds like great family teamwork. I wish my partner would entertain changing their diet to accommodate this (I've asked). I imagine the challenges of life are slightly more tractable when you genuinely deal with serious adversity as a family unit.

I understand it means an extra burden for all; but to me, voluntarily doing something challenging together for a family members' benefit seems preferable to facing each adversity largely independently.

As an aside, while likely much better than uncontrolled, 6-7% A1C still seems on the high end for lifelong. You probably already know this, but exercise immediately after carbohydrate consumption can also help - e.g. family walk after dinner (another thing my partner isn't interested in)

Although it's possible for someone with type 1 to have an A1C below 6%, it's very difficult. I've known a few people like that, and they are all super users. It's also going to depend somewhat on the lab running the A1C test, personal biology (A1c is not only affected by blood glucose levels) etc. 6-6.5% is superb control! Parent should be very proud. 6.5-7% is still very good, I haven't looked at the distribution of A1c's for T1D recently, but that would be much better than median which I think is above 8%.

Especially with kids, it's difficult since you don't control how much they decide to eat making pre-bolusing meals challenging (part of why reducing carbs tends to be helpful for people is it reduces the need to pre-bolus and makes it less risky since you need less up front meal insulin).