I’m in the market for a double stroller, with my first being 3 1/2 and #2 arriving any day. My issue is I can’t find a double stroller with a toddler seat tall enough for my toddler. He’s 35lbs, so within the weight limit for many seats, but none of them have a height extendable canopy that will fit over his head. He’s not THAT tall. Our single stroller has plenty of head room. Am I missing something??
Double strollers are in general smaller in space - it is because if the seats were full size (or larger), and many even want reversible ones, the stroller would become so heavy / wide / bulky that it wouldn't fit any normal doorway nor any normal car trunk. There were such, but people stopped buying those, and manufacturers rather made the seats smaller.
If fitting your 3.5yo is a priority, you will need to look at side-by-sides (not tandems, which are normally smaller as they are reversible seaters), and those side-by-side double strollers should be only forward-facing to actually have enough space for your toddler. I can strongly recommend looking at the Baby Jogger City Mini GT2 Double (or Baby Jogger City Mini Double2, or the alco Snap Duo which is simple but really effective.
Maybe the Bumbleride Indie Twin is also worth checking out, a very nice double pushchair.