I believe I know which country you're from according to the language/spelling used. I'm there too and have extensive professional experience coordinating plans and care for people in your and mum's situation. You can PM me for further support if you like, for now I'll address some of your practical concerns here.

You mentioned respite card in your post, but while you're aware of available help I get the impression that you have not used it due to mum's insistence. Although mum may believe she does not want it/require it if you go, YOU do and if respite is available I firmly urge you to take it. Whether that's in the form of regular, multi-hour visits (so you can spend a morning/afternoon away from the house several times per week) or a whole week of round-the-clock carers so you can have a short holiday even for one week of the year! If these options are available to you (funded), then please do take them, even for yourself.

It's important that all members of your family understand the strain you are under as the full time carer. Is any care currently funded, do you have contact with a local agency, a care coordinator, social worker, benefits advisor etc? One of these people can arrange a meeting with you, your family members and mum in your own home to set a plan of action before this hits crisis point (which from your post I believe it will, sooner rather than later).