Top tread is missing a landing tread so there's no overhang.
Skirts were done done with plywood for some reason leaving the end grain exposed, best way to cover it up add base cap moulding for a finished look.
Google it.
Like Joe said, I think the best thing to do is cover it with new wood, it will be a lot easier than trying to fix what you have. Looks like you have plenty of room so it wouldn't look covered.