The Bumbleride Indie Twin is listed at a slim 29 inches wide, as is the Bugaboo Donkey. I measured the Indie Twin as 29.5 inches at the widest protrusion (the latch that holds it closed when it's folded). The Donkey frame itself measures just a smidgen over 29 inches, but the canopy clamps tilt to the side just enough to make it closer to 32 inches wide
Let's see how this works out:
The door from my house to my garage is 32 inches wide, but functionally only 29.5 inches wide when open.
Bumbleride Indie Twin
The indie twin squeaks through, but just barely and it does scrape a little on the sides.
Bugaboo Donkey
The Donkey almost makes it through, but hangs up on the canopy clamps
Once I pull the canopy clips inward, the Donkey slides through as well
So now you're asking yourself, "does the difference really matter?" It really depends upon where you plan to use your stroller and the accessibility of doors and building where you live. Newer buildings, designed with ADA regulations in mind, tend to be very stroller friendly. On the other hand, if you plan to do a lot of shopping in a historic district, using a double stroller may be more challenging.
The Bugaboo Donkey does have the added bonus of being able to switch into mono mode, making it under 24 inches wide
In mono mode, it will fit easily through any doorway and you have the handy side basket for shopping
Converting it back and forth, however, is not something I would want to do every day. There is no place to store the second seat, so while it's relatively simple to switch it into mono mode, it's not something you want to do on the fly when you can't get through a doorway.