valdali you don't need to pussy-foot around your sil. At the same time you don't need to take on co-ordination responsibility because your OH is a workaholic. You have been bullied so are likely to be unassertive. This is something you would have likely developed had you given yourself a little bit of care and sought counselling to help you through the bullying. My advice would be to tell it straight to your sil and do the same thing with your OH - preferably if you can get them both in the same room at the same time and frankly as it's about their mother's future and ability to fund a care home via the sale of her house, that should be something you can insist on. You need to stand up for your own time and and energy. If you're prepared to do the admin, etc., they must be prepared to respond to you in a timely and constructive fashion and you should tell them that.
Lack of public toilets in towns.