How tall are the seat backs? Are the canopies adjustable for tall children?
You'll find the seat measurements (those that we could get our hands on 😉) in the Seat Unit part of the stroller specifications. The seatback of the Gazelle S seat is 46 cm, and the canopies are, unfortunately, not height-adjustable. You can open and extend them but can't slide them higher than they are.
As most reversible double/twin/sibling strollers and also a stroller system/combination, Cybex Gazelle S's seats are not the largest and are on the narrower side, so they'll last less (about maybe 2-2.5 years, if your kids are smaller, might last up to three years old).