Bit late to this but those look like steel rims - so I would definitely swap them. Trying to Brake with steel rims is the rain is absolutely terrifying! Pull as hard as you want and you just keep rolling... If those Weinnmans are 750s you should have enough reach for a 700c wheels. Much better tyre choice in 700c too. I wonder if you might be able to fit a third brake to the bridge the rear mudguard is attached to? It could be controlled by the stoker for emergency use. I'd also recommend fitting Kool Stop V2 brake blocks.
Bit late to this but those look like steel rims - so I would definitely swap them. Trying to Brake with steel rims is the rain is absolutely terrifying! Pull as hard as you want and you just keep rolling... If those Weinnmans are 750s you should have enough reach for a 700c wheels. Much better tyre choice in 700c too. I wonder if you might be able to fit a third brake to the bridge the rear mudguard is attached to? It could be controlled by the stoker for emergency use. I'd also recommend fitting Kool Stop V2 brake blocks.