I have no suggestions, but you have my absolute sympathy. It's looks awful.
I think people just have a completely different idea about what is acceptable or good workmanship in Thailand. I guess the lack of critical thinking, apathy, aversion to criticism, potential for anyone to blow their top over the slightest perceived insult, etc., lead to very poor workmanship being tolerated.
I don't know how anyone can look at what is in your pictures and think that that is OK.
I hope there is a way that you can fix it and maintain your familial bridges.
If it wasn't fixable, I would be thinking about ways to cover it up. Some sort of shelf with an overhang, a valance that hangs down and covers the horror, pictures, sachets, towel rails, etc..