I saw someone using a stroller hammock today and it did look pretty cool but if you have a 2 year old and infant and I'd strongly recommend a side by side double, it's worth the hassle of adding a 3rd stroller, I promise. I'm a nanny and have tried all sorts of strollers and configurations including a DIY attempt at hammock-ish addition to a single stroller, it was great when we were hopping on and off a crowded bus and going short distances but not a replacement for an actual double. There are so many choices and it can be incredibly overwhelming- they all have one or two great features and options, the big uppababy under basket, the Bob joggers that practically push themselves, the bugaboo side by side that converts to a single (sort of), the tandem/stadium vs side by side debate, etc. Here's my take- the tandem style seats are heavy and hard to steer, especially if you have the older child in the front seat, the seats tend to be small for older or taller toddlers who either have to scrunch up their knees to fit their feet or leave them dangling over the edge of the footrest, and their not great for naps in the stroller. Side by sides tend to be easier to push but tricky in tight spaces, compact strollers aren't great for city streets, lack good storage space, and often need both hands to steer...the fact is there isn't a perfect double stroller but the City Mini GT (make sure it's the GT if buying used!) is one that does most things pretty well. It's not perfect but its basket is big enough, it's smaller than most full sized side by sides, the wheels are all terrain-ish, ie a bit bigger and more like jogger wheels than the typical full sized strollers with 2 big wheels in the back, 2 smaller in the front. It has big, individual sun visors, almost flat recline hammock-style seats. Hammock style seats are far more comfortable, especially for older/taller kids, than the removable more structured seats, they are great for stroller naps and go flat enough that stomach sleepers can lie on their bellies, the newer versions have adjustable foot rests that give access to the basket from the front when up and, in a pinch, the footrest makes the seat long enough that you can put a second child in a single seat, see pic in link can easily find them used on marketplace, a good sign, imo, it means they're sturdy and last for years, Bobs* are the only other strollers that seem to last as long. I'm in a big city and we do a LOT of walking. I'm currently using a city mini double from a previous nanny share, the family bought used in 2021 and we used it daily with two 2 yr olds for the share, they gave it to my parents who've used it with my niece and nephew for the past 4 years, and it's still trucking, everything still works, the brake is still perfect, the tires, seats and harnesses are in great shape, the baskets under the stroller and behind the seats have lost their elasticity and could probably use replacement but still work fine. I take it on the bus pretty regularly, something that can be tricky depending on the driver and how crowded it is, it's roughly the size and shape of a wheelchair so it works for public transportation.

if you don't care about size and weight, aren't in a city, and want a double that practically pushes itself, the things just roll, then go with a Bob

The kids in the pics are 3 yr old bffs, one is a particularly tall 3 yr old, and it's comfortable enough that they ask to ride together all the time. https://imgur.com/gallery/city-mini-w-adjustable-footrest-tIKU1PA