Surely when your mum is no longer around the reason for the stress between you and your sister will be gone. I think a family WhatsApp is a good idea, we have one and I happened to find out our three children have one of their own which I think is great and I hope they will keep an eye on me if necessary. My brother and I split the care of mum between us, you can't know everything about everything. Having said that your mum is enjoying her secret life I think.
Scottish political mess. Is Devolution working?