Elderly inlaws could definitely benefit from having a large walk-in shower (rather than their current shower over bath arrangement) but as they only have one toilet and one bathroom (the toilet is in this one bathroom) - surely a wet room is a slipping hazard for every other time they need to use the bathroom?
The bathroom is a decent size. They could have the bath taken out and an enclosed shower cubicle installed, which would ensure the rest of the room especially the floor stays dry. Why hasn't the plumber suggested this, are wet rooms more expensive?
Am I missing something here that's not obvious?