Seems ok for you. Main thing is active focus. Sometimes making a small change to diopter use or close-up distances can help build that habit.
Remember, vision tends to only improve with some amount of blur > focus challenge.
Yes that differential for the 11 year old can work. Main question is, how to build that into her close-up habits. Mostly a parenting question. Ideally making it fun, a game, building a solid habit. Should be playful and positive.
Same for 15 year old. The name of them game is getting them to participate. If need be better to not push that so they don’t get into some teenage thing of doing the opposite of what you want. 😂