Shared nodes can be difficult to edit later see this Q and A https://help.openstreetmap.org/questions/5352/should-the-edges-of-landuse-or-boundary-areas-share-points-with-streets-that-form-their-borders

I am sorry to here of your loss. Mike, like me, may not have met any other mappers. Over the years I have been contributing I have had a few messages of help, advice and sometimes why have you done it like that? but I don’t know them. I have had two close encounters. I attended an open talk in a Cambridge university building about climate and co2 and some students were selling Fredrick Ramms OSM book, so i guess they may have been mappers but foolishly didn’t ask. and I wish I’d brought the book!, and also near Cambridge while on a walk a Rambler friend said an acquaintance of hers in the Cambs Cycling group and a cycle map maker, who’s good work I had noticed, and who had queried one of my mapping errors. had been in the pub that lunch time. So good luck with your search. I am sure your Dad enjoyed his mapping as much as I do and I see he made quite a lot of contributions, they will be an additional memorial to him.

I posted a question on using the environment agency river levels web site sometime ago. By adding the elevations of car parks and riverside paths and for passable roads they could be assessed by monitoring the level from the Environment Agency . It may only work in flatter areas. see https://help.openstreetmap.org/questions/18032/ways-and-water-levels-in-gb