Hello
@schwenner57 and welcome
Unfortunately it seems to be extremely common in families that one of the family becomes the carer and the rest of the family do nothing apart from imparting "helpful" advice 😒
If you are in UK then it is not the family that has the "duty of care" - it is Social Services, so your wife has every right to refuse to care. Practically, though, it is very difficult to continue this when everyone around you is assuming that you will do it.
If your wife does end up as her mothers carer then do things like make sure that you and she have POA for finances and health - if you dont have this then it will become impossible to do the caring as the dementia advances. This is one area to really put your foot down. Also, get outside, professional help as soon as it is needed (probably sooner than you think) and dont refuse to consider a care home when the time comes. Looking after someone with dementia is extremely hard. You and your wife will need respite and space to recover - carer burnout is a real thing.
If the rest of the family do not help with day to day caring then they will not have earned the right to tell you what you should and should not do, so ignore any "advice". And if they complain about how your wife is caring and the decisions being made then tell them that if they are unhappy then they are welcome to care for her themselves.