Hiya and Welcome
Ditto all that Jennifer had to say in spades, especially the 'all consuming'.
When we get together with my brother and SIL we always start off with making the rule, 'ok no talking about mum and AD', well, the 'rule' never lasts longer than 5 minutes. We all agree mum is the first person you think of when you wake, the last when you go to sleep, and all hours in between.
Have you considered getting dad into day care, even if its only for a few hours a week, once a week. Doesn't have to be anything to do with AD if dad is in the early stages, try calling Social Services, Age Concern to see if there is anything in your mum's area.
My mum used to go on a Friday 10:00 - 3:00, she loved it, different people for her to talk to (I sometimes think mum used to get fed up with seeing just the family, as much as (and I hate to say this), we get fed up seeing her (Ouchhhhh).
It would give your mum a few hours to be just herself, go out without worrying, or just sit at home reading a book can be bliss. My mum was not at all keen on going originally, she didnt want to sit around with all those old people (she's 88!), so my SIL went with her until she settled and made some friends. Sadly she can no longer go, but it was great while it lasted. Just those few hours made all the difference, something to look forward to, those few 'no responsibility' hours a week.
Keep smiling.
Love
Cate