It’s not quite what you are looking for, but see if the Maya wrap for babies might work. It goes across the chest and you wrap it around a metal ring (it’s really easy once you try it a few times). I know it would work for one dog for sure, but I am not sure about 3. It has a pocket at the end and it’s made our of durable cloth.
Edit: And if you do end up getting it, go for the brand name one (Maya).