In that case, all you can do is control how you deal with the situation and that might well meaning that you withdraw from it.
I don't know quite how it all works, but there are cared for people in Fife who have had automated toilets installed by social work - I think it works a bit like a toilet and bidet all-in-one. Apparently, they're used with very frail people who cannot wipe. I'm wondering whether that might be an option.
The fact that your mum is using a bidet is a bit alarming - they can be rather unstable, unfortunately, and often cause more bother than they're worth.
When Mum was in her own place, Homecare wanted me to move her bed downstairs into the living room with a bed in case she fell on the stairs.
Instead, I had a stairgate put on (as Homecare requested), but at the top. I converted the 2nd bedroom into living room and Mum kept her own bedroom and access to the bathroom. Although Mum had severe mobility problems, she was still able to walk to the bathroom at that stage.
I was doing a short commute to work each day, driving to Mum's town - only about 14 miles away - to check on things and then driving back home, about 12 miles. (The worst was when DH had open heart surgery and I had to add on an hour's commute each way to the hospital, but Dad was still alive then, though he had medical issues of his own.)
Mum did need more help as her problems progressed. We managed to build on a wet room adjacent to her bedroom in our house, but she did need help in there.
At the time, I didn't know about the automated toilets that I've mentioned.
I took care of her care between 8 pm and 7 am as well as dealing with all DH's care.
In your case, OP, nothing is going to change until you insist on it. You might have to force your mother and brother into going down the carer route by withdrawing.